A couple of generations ago the Meditations of Marcus Aurelius was very fashionable reading. That was the time when every good publisher's catalogue included an elegant series of miniature classics; and there were very few of these in which the Meditations failed to make its appearance. The vogue has passed away now, but it may explain why the book is still known by name to so many people, even though acquaintance with its contents is rarer than it once was. Indeed, when you pick up this volume, you may well ask yourself, 'What is it going to be about? What sort of stuff shall I find inside it?' Let me say at once, then, that you need not expect any continuous or connected theme. This is simply the private journal or 'commonplace book' in which Marcus Aurelius jotted down from time to time anything that struck him as worth preserving. At one moment he is recording a thought suggested by some recent event or personal encounter; at another, musing on the mysteries of human life or death; now he is recalling a practical maxim for self-improvement, now copying a quotation from the day's reading which has taken his fancy. All these, and a wide variety of other items, are set down just as they occurred to the writer. You may take up the book or lay it down at any point you choose, and read as many or as few of the entries as suits your mood. Marcus, in short, has provided us with an excellent book for the bedside.
The Meditations is customarily, and no doubt rightly, classified by librarians under the heading of 'Philosophy'; but this may give the reader a misleading impression, unless he understands the place which philosophy held in the ancient world. From what he knows of the writings of its twentieth-century exponents, he is unlikely to conclude that its chief aim and end is the attainment of personal virtue. This, he imagines, is the province of religion, not of philosophy. But in classical times things were different. Morality, the good life, man's relations with the gods--all these were the domain of the philosopher, not the priest. Roman religion in the Imperial age had no concern with moral problems. Its business was simply the performance of such appropriate rites as would ensure the gods' protection for the State, or avert the effects of their displeasure. It was a formal system of public ceremonies carried out by State officials, and provided no answers to the doubts and difficulties of human souls. Yet then, as now, men found themselves perplexed by the great questions that are the common concern of us all. What is the composition of this universe around us, and how did it come into being? Is it ordered by blind chance, or a wise Providence? If gods exist, do they interest themselves in mortal affairs? What is the nature of man, and his duty here, and his destiny hereafter? It was not the priests but the philosophers who claimed to supply the answers to such inquiries. Their answers, it is true, were not unanimous; there were rival systems of philosophy, and each proffered its own solutions (as, for that matter, the different world-religions of our own day still do); but all were agreed that the sole right to pronounce with authority in the fields of metaphysics, theology, and ethics belonged to philosophy. It was believed to be competent to unfold the story of creation, define the unseen powers behind the world-order, expound the nature and purpose of human existence, prescribe the rules for right living, and reveal the future that lay beyond the tomb. Thus philosophy took the place which in our day is occupied by religion, as the instructor and guide of souls at every stage of their earthly pilgrimage. Such a claim is especially justified in the case of Stoicism, which was marked by a more religious character than any other ancient system. As the historian Lecky observes, 'Stoicism became the religion of the educated classes. It furnished the principles of virtue, colored the noblest literature of the time, and guided all the developments of moral enthusiasm.' 
What this amounts to is that a reader who wishes to approach the thought of Marcus Aurelius in the right way should remember that the emperor's frequent allusions to 'philosophy' always carry the kind of implications we associate nowadays with the word religion. For philosophy, to the man who wrote these Meditations, meant everything that a religion can mean. It was not a pursuit of abstract truths, it was a rule for living. In a sense, this book is as truly a manual of personal devotion as Thomas a Kempis's Imitation of Christ -- with which it has often been compared, and which is indeed its Christian counterpart.
The Stoic Philosophy
Stoicism, the system of philosophy in which Marcus believed, was originally a product of Middle Eastern thought. It had been founded some three hundred years before Christ by Zeno, a native of Citium (now Larnaka) in Cyprus, and received its named from the 'Stoa', or colonnade, at Athens where he was accustomed to discourse. His chief disciple was Cleanthes, who in turn was followed by Chrysippus; and the successive labors of these three men, who were afterwards held in veneration as the 'founding fathers' of Stoicism, had resulted in the formation of a scheme of doctrine embracing 'all things divine and human'. The three keywords of Zeno's creed were Materialism, Monism, and Mutation. That is to say, he held that everything in the universe -- even time, even thought -- has some kind of bodily substance (materialism); that everything can ultimately be referred to a single unifying principle (monism); and that everything is perpetually in process of changing and becoming something different from what it was before (mutation). These three tenets were the bedrock on which Zeno built his whole structure. His uncompromising insistence upon them led him occasionally into propounding ideas that were clearly indefensible; but in the hands of his successors the more rigid assertions of the founder were modified and softened in such a way as to make them acceptable to thinkers of a more realistic turn of mind.
When Stoicism passed from the East to the West and was introduced to the Roman world, it assumed a different aspect. Here it was the moral elements in Zeno's teaching that attracted the chief notice, and their practical value was promptly appreciated. A code which was manly, rational, and temperate, a code which insisted on just and virtuous dealing, self-discipline, unflinching fortitude, and complete freedom from the storms of passion was admirably suited to the Roman character. Consequently, the reputation and influence of Stoicism increased steadily all through the centuries which saw the decline of the republic and the rise of the principate; and by the time Marcus Aurelius ascended the throne it had reached the height of its supremacy. Its conceptions and its terminology were by now familiar to educated men and women in every important city of the empire.
The Stoics defined philosophy as 'striving after wisdom'; and 'wisdom' in turn was defined as 'the knowledge of things divine and human'. They divided this knowledge into three branches: Logic, Physics, and Ethics." Since the first requisite in the search for truth is clear and accurate thinking, which itself depends upon a precise use of words, and a vocabulary of technical terms, the initial study was Logic. After that came the investigation of natural phenomena and the laws of nature. This extended up to the metaphysical interpretation of the universe; for in the Stoic scheme Physics included the complete study of Being in its threefold manifestation--man himself, the created universe around him, and god. Last of all, holding the highest and most important place in the system, came Ethics. For the real business of philosophy, the point towards which all other inquiries converged and to which all other branches of knowledge were subservient, was the proper conduct of man, defined in a word as 'virtue'. As Diogenes Laertius puts it, 'they compare philosophy with a living creature; its bones and sinews corresponding to Logic, its body of flesh to Ethics, and its soul to Physics. Or again, they liken it to a fruitful field, of which Logic is the surrounding fence, Ethics the crop it bears, and Physics the soil.'  It will be convenient to summarize briefly their teaching on these three subjects.
(a) Logic. In the department of Logic, all that the reader of Marcus Aurelius need be acquainted with is the Stoics' theory of knowledge and of the means by which it is attained. In their system knowledge begins with impressions, which are produced by the impact of things or qualities on the senses. It is then in the power of the mind to pass judgment on what the senses report: to assent to it as a truthful presentation of objective reality, or to reject it as false. (The critical importance of this step is stressed repeatedly by Marcus.) Some impressions, of course, will command immediate and spontaneous assent--for example, the elementary notion that good is beneficial and evil harmful--but in other cases assent is given only after deliberate reflection; and it may vary from a hesitant approval, so weak and faltering as to constitute a mere 'opinion', up to the positive assurance that is produced only by a so-called 'arresting impression'. This is an impression so strong that, in the words of one writer, it 'seizes upon the subject, as it were, by the hair and extorts his assent'. Nevertheless, even an impression of this kind may in fact be imperfect or misleading; and consequently the assent founded upon it, no matter how assured, may be mistaken. It must therefore next be submitted to the scrutiny of reason, the sovereign power which alone can issue the passport to conviction. Finally, this personal conviction must be verified by comparison with the experience of past ages and sages, and confirmed by the general verdict of mankind; and it then becomes knowledge. In explaining these four stages, Zeno used to illustrate impressions by the outstretched fingers, assent by the closed hand, conviction by the clenched fist, and knowledge by the fist gripped tightly in the other hand.
(b) Physics. Stoic physicists taught that the primordial source of Being in all its forms is a certain substance, omnipresent in the universe, which can best be described as Mind. However, since they were thoroughgoing materialists, this Mind was held to consist of a real and positive stuff, though of the thinnest and most impalpable kind imaginable. Borrowing an analogy from the subtlest and most lively of known elements, and one which also nourishes life and growth, they conceived its essential nature to be that of Fire; but a Fire so rarefied and ethereal that the word 'heat' perhaps comes closer to describing it than anything which might suggest ideas of actual flame. This Mind-Fire, which possessed consciousness and purpose and will, was both the creator and the material of the universe; it took shape in innumerable different manifestations, so giving all things their particular substances and forms, and producing out of itself the visible world and all within it. According to the various contexts in which he is thinking of it, Marcus has many names for it: when he dwells on its operations upon the universe as a whole, he may call it God, Zeus, Nature, Providence, Fate, Necessity, or Law; as one of the material elements in nature it is Fire, or Air, or Force; in relation to the constitution of man himself, it becomes Soul, Reason, Mind, Breath, or (in the technical language of Stoic psychology) 'the Master-Faculty'. It is important to remember that all these words are simply terms for the same creative Mind-Fire in its varying aspects.
Stoicism is thus a pantheistic creed: that is to say, it holds that god is immanent in all created things, but has no separate existence outside them. As such, it is in direct opposition to the rival teachings of Epicureanism. Epicurus, developing the ideas of Democritus, maintained that the only constituents of the universe are atoms and empty space. Atoms in infinite numbers are in continuous high-speed movement in the void, and their fortuitous collisions lead to certain combinations which make the world what it is at any given moment. Since this ceaseless clashing of atom with atom in the vortex is forever giving rise to new combinations and dispersions, the life of the universe continues to perpetuate itself inexhaustibly. It is true that among the infinitely numerous possible combinations some are bound to look as if they were the result of design; but in reality there is no such thing as design, and all is due to chance. Marcus himself, in more than one passage of the Meditations, considers the implications of this alternative theory. 'Is there a wise Providence, or only a jumble of atoms?' he asks; but it is only to conclude that in either case the moral issues with which he is concerned would be unaffected. For his own part, his conviction of the providential guidance of the world does not waver.
To explain the process of creation, the Stoics relied on the theory of tension. From the fact that most bodies expand when heated, it is clear that heat exerts pressure. Accordingly the Mind-Fire, in its primal state of intense heat and correspondingly high pressure, at once begins to expand; and this brings about a proportionate slackening of tension. As a result, some of the divine fire cools and becomes visible as the humbler element of earthly fire; this again, as the tension continues to weaken, partially condenses into air; and portions of the air, in turn, solidify into water and earth. At this stage a movement in the opposite direction sets in; the vital heat contained in these four elements begins to assert its creative energy, and to materialize in the countless shapes and forms which compose the universe. Physically, these are differentiated by the varying proportions of fire, air, earth, and water contained in them; in other respects, their nature depends upon the degree of tension in the generative fire. Thus at a certain grade this force will realize itself as the organic forms of vegetable life; at a higher degree as the animals or 'souls without reason'; and after that, as the 'reasoning souls' distinctive of men. Within these categories as many different forms of being can be produced as there are differing degrees of tension. At the maximum tension, the Mind-Fire takes on the attributes of a World-Soul, holding the same relation to the universe as the individual soul to man himself. At long last, however, a time comes when this ever-mounting energy reaches a pitch of intensity at which it becomes the devourer of its own creation: one after another the different forms and substances dissolve back into their original elements, the water evaporates into air, the air turns to flames, and finally the universe disappears in a grand conflagration which leaves nothing surviving but the primordial Mind-Fire itself. Thereupon the whole process straightway begins again; the successive acts of creation repeat themselves, and the pattern of history starts to unroll as before. All this recurs in endless cosmic cycles of alternate creation and destruction; and since the eternal laws are unchanging, after each conflagration every event that has happened in previous cycles must reproduce itself once again down to the smallest detail.
As for man himself, he is a microcosm reflecting faithfully in itself the vaster organism of the universe. His physical body is formed out of the four elements, and that which creates, indwells, and controls it is a particle of the omnipresent Mind-Fire. Just as this fiery Power at its highest and purest acts as the soul of the world, so here, residing in the body in a scarcely less ethereal form, it plays the same part for man, generating and directing his life, his senses, his thoughts, and his emotions. It is nourished by the blood, and has its seat in the heart, the chief centre of the blood. (Hence Marcus twice refers to the soul as 'an exhalation from the blood'.)
At the appointed time Nature disperses the material elements which have composed the body, in order to use them for other purposes; and this is what we know as death. As to what happens to the 'fiery particle', Stoics, like Christians, are not unanimous. All agreed that it must sooner or later be reabsorbed in the primal Mind-Fire, but there were differences of opinion as to when this took place. The earliest doctrine, to which Marcus adheres, was that after the dissolution of the body and the soul lived on in the upper regions of the air, and was not resolved into the World-Fire until the final conflagration. This was the teaching of Cleanthes; Chrysippus, on the other hand, opined that it is only the souls of the good and wise which thus preserve their personal identity until the end of the world, the bad and unwise being allowed but a brief period of survival before their re-absorption. Other teachers held that in every case this re-absorption followed immediately on death; and others again believed in a purgatorial state in which the soul underwent physical and moral purification as a prelude to its reunion with the world-substance.
(c) Ethics. The Stoics taught that the chief end of man, and his highest good, is happiness. In their view happiness was attained by 'living according to Nature'. This celebrated phrase is too easily misunderstood by the modern reader. It does not mean living the simple life, or the life of the natural man; still less does it mean living just as one likes. To grasp its significance, we have to remember that 'Nature' is one of the Stoic names for the divine fire which, besides creating all things, also shapes them towards their proper ends. Thus it embodies the idea which we nowadays express by the term 'evolution'; the American poet who wrote 'Some call it Evolution, and others call it God' came very near to the Stoic way of thinking. It was the force which guided and directed every kind of growth or development towards its ultimate perfection; and because it was also a force that was alive, purposeful, and intelligent, the Stoics themselves did in fact sometimes call it God. 'Live according to Nature', then, was a maxim not very different from the New Testament injunction, 'Be ye followers of god', and implied an equally lofty ideal and an equally arduous discipline.
If we ask for a more precise definition of this 'Natural Life', Marcus says that it consists for every creature in a strict conformity with the essential principle of that creature's constitution. In the case of man, this essential principle is his reason, which is a part of the universal Reason. In so far, therefore, as he follows this rational law of his being, he approaches happiness; in so far as he departs from it, he falls short of happiness. The Natural Life, in fact, is the life controlled by reason; and such a life is briefly described as 'virtue'. It is this meaning of virtue which explains the Stoic dogma that 'virtue is the only good, and happiness consists exclusively in virtue'.
Reason tells us plainly that some things are in our power and others are not. For instance, bodily health, wealth, friends, death, and such like are not ours to command; therefore they can be neither helps nor hindrances to the Natural Life. They are 'things indifferent'. But our own will, our judgments, our power to accept what is morally right and to reject the contrary--all these are in our power. It follows that nothing external can by itself affect us; it is not until we inwardly assent to it or refuse it that we can be harmed or benefited. Pleasure by itself is not a good, nor pain by itself an evil; they become so only if we judge them to be so. This is the meaning of Marcus's insistence that 'opinion is everything'. It also explains the wise man's readiness, which we find emphasized so often in his pages, to 'accept without resentment whatever may befall'; a precept which is clearly one of the mainstays of his own personal life. This is the principle behind the famous 'apathy', or passionlessness, of the ideal Stoic sage. Such a one, the philosophers taught, will experience all the sensations and emotions which are the common lot of man, but because he refused to view them as evils they will not perturb him. Regarding them as things external and therefore indifferent, he remains secure and unharmed. Consequently, as the Stoics paradoxically asserted (to the amusement of the Epicurean poet Horace), the wise man alone is the true king, rich in spite of his poverty, happy in spite of physical torments, free even if a slave, serene and self-sufficing through all vicissitudes. Should circumstances ever prove too much for this perfect detachment, he will not hesitate to take a voluntary departure from life; for mere life by itself is also among the things that are indifferent. Both Zeno and Cleanthes died by their own hands, and we shall find Marcus himself more than once toying with the thought that in certain conditions it better becomes a philosopher to leave life than to remain in it.
As unequivocal as man's duty to himself is his duty to others. Since all men are manifestations of the one creative Mind-Fire, the doctrine of universal brotherhood played a leading part in the Stoic system. The rational and social instinct is something that is inherent in the constitution of man. Kindness to his fellow-creatures is therefore at all times incumbent upon him; he must school himself to be tolerant of their failings, make allowance for their ignorance, forgive their misdoings, and help them in their need. To Marcus this was not always the easiest of tasks; the very frequency with which he reminds himself that neighborliness is an important part of the Natural Life suggests that in practice it was sometimes a strain on his powers of benevolence. Nevertheless, he recognizes to the full that man is a social being, made for social action. He accepts the Stoic axiom that the whole universe is an organized society; a civic community in which the divine and the human dwell together in a common citizenship. (Earlier, the Cynics had described it as the cosmo-polis: the city which is co-extensive with the whole cosmos.) In his own words, 'the world is as it were one city'; and just as to the Athenian Athens was the 'dear city of Cecrops', to the philosopher the universe is the 'dear city of God'.
Marcus Aurelius Antoninus
Marcus Annius Verus, the future ruler of Rome, was born on 26 April A.D. 121, in the reign of the emperor Hadrian. His father, Annius Verus, was a roman nobleman; and his grandfather, of the same name, had been Prefect of the city and three times consul. Both his parents died young, and on his father's death Marcus was adopted by his grandfather, of whom he writes with warm affection and respect. The years of his boyhood were happy and studious; a series of the ablest tutors cared for his education and trained him in the doctrines of the Stoic philosophy; and though his health was never robust he enjoyed riding, hunting, wrestling, and outdoor games. When he was seventeen the emperor Hadrian died and was succeeded by Aurelius Antoninus (usually known as Antoninus Pius), whose wife was Marcus's aunt Faustina. Having no son of his own, Antoninus adopted his wife's young nephew, changed his name to Marcus Aurelius Antoninus, named him as his successor, and betrothed him to his daughter Faustina. How much happiness Marcus found in this marriage must remain an enigma. The contemporary chroniclers delight in retailing stories of her shameless profligacy, and declare that she was treated with culpable indulgence by a husband far too good for her. However, the evidence for this is doubtful; and it is certain that when she died, thirty years later, Marcus grieved for her loss. She had borne him five children, of whom he was passionately fond; but death robbed him successively of all of them except the worthless Commodus, who lived to succeed his father.
From his seventeenth to his fortieth year, as the close companion and colleague of Antoninus, Marcus was occupied in learning the arts of government and preparing himself for the future duties of empire. In those years, the majestic immensity of the pax romana, maintained by the Imperial administration, stretched over the whole of western and southern Europe, north Africa, Asia Minor, Armenia, and Syria. But much of the burden of governing this vast dominion centered on the person of the emperor himself; and when Antoninus died in 161, a heavy weight of responsibility descended on Marcus. Against the wishes of the Senate, he took Lucius Verus, the other adopted son of Antoninus, as his colleague on the throne; and Rome was presented for the first time with the spectacle of two emperors. Almost simultaneously came the end of the long years of Imperial serenity. An outbreak of plague spread disastrously over the western world. Floods destroyed great quantities of grain at Rome, obliging Marcus to sell the royal jewelry to relieve his starving subjects. In addition to the anxieties of pestilence and famine he found himself harassed by the alarms of war. Peace was broken by the clash of arms; on the eastern frontiers fierce tribesmen of the Marcomanni ('men of the marches'), Quadi, and Sarmati poured over the border in a series of determined attempts to pierce the Empire's defenses. Faced by this threat, Marcus left Rome in 167 to take command in person of his hard-pressed legions on the Danube. In 169 Verus died, and for most of the next thirteen years Marcus remained alone at the post of duty. For a brief interval he was called to Asia, where the commander of the troops, Avidius Cassius, revolted and caused himself to be proclaimed emperor. But Cassius was murdered by two of his officers; and it is characteristic of Marcus that when they brought the severed head to him he recoiled in disgust and refused to see them. He ordered all the papers of Cassius to be burnt unread, and treated the rebels with clemency. During this expedition to the East his wife Faustina, who had accompanied him, died; and Marcus returned to the Danube to resume his task of holding back the onrushing tide of barbarism. There, among the misty swamps and reedy islands of that melancholy region, he consoled the hours of loneliness and exile by penning the volume of his Meditations. Laborious years of toil and conflict had by now exhausted his spirit; he was weary of life, and in his own words 'waiting for the retreat to sound'. When at last an infectious disease attacked him in the camp, he lingered for a few days and died on 17 March 180, in the fifty-ninth year of his age and the nineteenth of his reign. 'Weep not for me,' were his last words; 'think rather of the pestilence and the deaths of so many others.'
To suggest that Marcus was not a true Stoic seems paradoxical. Nevertheless, his meditations indicate a type of character that would hardly have satisfied Zeno or Chrysippus. The varying moods of hope and depression, the sensitive shrinking from disagreeable associates and sights of blood, the repressed but evident longing for sympathy and affection--these are not the signs of a temper cast in the antique Stoic mould. The truth is that Marcus represents a transitional phase of thought. In place of the old assurance of self-sufficiency there is a diffidence and a readiness to acknowledge his own failures; instead of the Stoic virtue of pride he seems to anticipate the Christian virtue of humility. All the more, then, do we sympathize with his recurrent struggles for self-mastery, and his efforts to direct every natural impulse and emotion into the stern service of duty. No doubt this constant preoccupation with the perfecting of self, this reiteration of improving maxims and moral platitudes, has produced a distasteful impression on some readers; and there have even been detractors who have called Marcus a humbug and a prig. Such a judgment, I think, shows a failure to understand the nature of the religious temperament; for when a man takes his religion seriously, conscientious self-scrutiny and aspirations to virtue are bound to form a very large part of all his inward thoughts and meditations. After all, the writings of a St. Paul or a Thomas a Kempis exhibit as many moral admonitions, exhortations to sanctify and citations of canonical authorities we find in Marcus; yet no one has had the hardhihood to accuse their authors of insincerity--even despite their avowed intention to write for the edification of a large circle of readers. When, on the other hand, we overhear the philosopher-emperor's secret communings with his own soul, and remember that at no time is he addressing any human auditor but himself, I believe every instinct tells us that we are in the presence of a man who is simple, humble, and utterly sincere.
One small but significant fact, which so far as I know has not been noticed by any of his editors, seems to indicate his genuine goodness of heart. When he has occasion to refer to persons in terms of approval, he never fails to record their names. But when, as sometimes happens, he allows himself a comment that is unfavorable, a veil of secrecy is drawn over the offender, and we are left with no more hint of his identity than is furnished by an unrevealing 'he' or 'they'.  This charitable habit--which might perhaps be commended to some who write their memoirs in our own day--deserves particular notice in one whose sensitivities must have suffered almost daily affronts from the manners and society of the period.
'Lead me, Zeus and Destiny,' says the prayer of Epictetus, 'whithersoever I am appointed to go. I will follow without wavering; even though I turn coward and shrink, I shall have to follow all the same.' The words fitly express Marcus's attitude to life. If he remarks wryly that it is 'more like wrestling than dancing', his fortitude does not fail, and the peculiar sweetness and delicacy of his character have an attraction that is not lessened by this tincture of gentle pessimism. 'By nature a saint and a sage, by profession a ruler and a warrior,' from the lonely height on which he stands he contemplates the sorrows of mortality with eyes that are disillusioned yet serene. 'And so', to quote Matthew Arnold's tribute,' he remains the especial friend and comforter of scrupulous and difficult yet pure-hearted and upward-striving souls, in those ages especially that walk by sign, not by faith, but yet have no open vision: he cannot give such souls, perhaps, all they yearn for, but he gives them much, and what he gives them they can receive.' And of his equestrian statue which stands in the Piazza Campidoglio in Rome, Henry James has written that 'in the capital of Christendom, the portrait most suggestive of a Christian conscience is that of a pagan emperor'.
So long as men are attracted by the tears and triumphs of human goodness, Marcus Aurelius will not lack readers. Wistful, compassionate, and disenchanted, this last of the Stoics still puts our weakness to shame and our discontent to silence.
Stoicism and Christianity
In conclusion, the reader may usefully be reminded that the theology of the Christian church owes a large debt to Stoicism. In the original gospel of Christ the moral and spiritual elements predominated, and the intellectual element was wholly subservient to them. But when the message spread beyond the confines of Palestine, and its implications were assimilated by thoughtful men in other lands, the need for more exact conceptions of the truth made itself felt. It became evident that the new faith must raise a multiplicity of questions in the fields of cosmogony, metaphysics, psychology, and ethics; and for all of these the church had to discover some coherent system of answers. Fortunately, much of the material for the task lay ready to hand. The ground had already been explored by the schools of pagan philosophy, and their findings constituted the accepted body of contemporary scientific knowledge. Many of the men who flocked into the Christian community during the second century had been educated in these doctrines from their youth; the majority of them in the principles of Stoicism, since that system more than any other attracted the naturally religious type of mind. To them, therefore, the churchmen turned for aid in building the structure of their theology. This is not to imply an uncritical or wholesale appropriation of the pagan ideas. Rather, when a philosophical theory seemed to suggest the lines along which Christian thought might seek its own solution of a problem, it was taken as a working hypothesis and tested for its possibilities; after which, in a suitably modified form, it might find its place in the new religion. In the words of Dr. Prestige, 'the idea was cut to fit the Christian faith, not the faith trimmed to square with the imported conception'. 
For example, the author of the fourth Gospel declares that Christ is the Logos. This expression (meaning either 'reason' or 'word') had long been one of the leading terms of Stoicism, chosen originally for the purpose of explaining how deity came into relation with the universe. According to the philosophers, the divine Reason had brought the world into existence through the agency of innumerable particles of itself, which indwelt and gave form to every created thing. This version of the origin of the universe, already deeply impressed upon his contemporary generation, was accepted in principle by the evangelist. He asserts, however, that the medium through which God manifested himself in the creation and maintenance of the world is not a multiple but a single and personal Logos, begotten of himself. 'In the beginning was the Word, and the Word was with God, and the Word was God. All things were made by him, and without him was not anything made that was made.  Thus Christian baptism is given to Stoic metaphysic.
Another Stoic concept which furnished inspiration to the church was that of 'divine spirit'. Cleanthes, wishing to give a more explicit meaning to Zeno's 'creative fire', had been the first to hit upon the term pneuma, or 'spirit', to describe it. Like fire, this intelligent 'spirit' was imagined as a tenuous substance akin to a current of air or breath, but essentially possessing the quality of warmth; it was immanent in the universe as God, and in man as the soul and life-giving principle. Clearly it is not a long step from this to the 'Holy Spirit' of Christian theology, the "Lord and Giver of life', visibly manifested as tongues of fire at Pentecost and ever since associated -- in the Christian as in the Stoic mind -- with the ideas of vital fire and beneficent warmth.
Again, in the doctrine of the Trinity, the ecclesiastical conception of Father, Word, and spirit finds its germ in the different Stoic names for the divine Unity. Thus Seneca, writing of the supreme Power which shapes the universe, states, 'This Power we sometimes call the All-ruling God, sometimes the incorporeal Wisdom, sometimes the holy Spirit, sometimes Destiny.' The church had only to reject the last of these terms to arrive at its own acceptable definition of the Divine Nature; while the further assertion that 'these three are One', which the modern mind finds paradoxical, was no more than commonplace to those familiar with Stoic notions.
Other instances of Christian ideas which had previously been taught by the Stoics are the conviction that men are 'God's offspring'  and partake of his nature, and the consequent belief that we should regard all men as our brothers and neglect no opportunity of benefiting a fellow-creature. One of the later New Testament writers has also stamped with Christian authority the Stoic belief in the final conflagration of the universe.  A notable Stoic contribution, too, to the manners of the Church, and one which has had a lasting influence, was the practice of asceticism. Christians who desired to follow counsels of perfection took the Stoic sage and his way of life as their formal exemplar. The coarse garment, the untrimmed locks and beard, were adopted as the badges of aspiration to sanctity. Just as the Stoic professor was accustomed to withdraw from society and meditate in solitude, his Christian imitators not only followed his example but appropriated his terminology. In the Stoic vocabulary one who went into retreat was an 'anchorite'; one who practiced self-discipline was an 'ascetic', those who lived apart from their fellows were 'monachi', and the place of their retreat was a 'monasterium'. Each of these borrowed expressions has retained its place and significance in the language of the church to this day.
Perhaps the best evidence, however, of the way in which Stoic ideas penetrated Christian thought is found in a treatise which became the basis of medieval moral philosophy, the Duties of St. Ambrose of Milan. Here the scriptural conceptions of righteousness and holiness are almost wholly displaced by the former doctrines of Stoic orthodoxy. The voice is the voice of a Christian bishop, but the precepts are those of Zeno. Not godliness, but happiness appears as the ideal of life; and the happy life is a life according to nature. Such a life is achieved by virtue, for virtue is 'the highest good' and virtue is once more resolved into its ancient pagan elements of justice, prudence, temperance, and fortitude. Most remarkable of all, the happy and virtuous life is declared to be fully realizable during our sojourn here on earth; and the hope of future bliss becomes not a primary but only a subordinate motive.
In the face of these and similar pronouncements by a prelate and doctor of the church, who will deny the right of Stoicism to be called, in the words of a writer of our own age, 'a root of Christianity'?
1. History of European Morals, vol. 1, p. 225.
2. Cleanthes subdivided them into Logic and Rhetoric, Physics and Theology, Ethics and Politics.
3. Diogenes Laertius, vii. 40.
4. e.g. III, 15, iv, 6; iv, 28; viii, 52; xi, 14.
5. God in Patristic thought, p. xiv.
6. John i:I.
7. Quoted by St. Paul (Acts xvii:28) from the Hymn of Cleanthes.
8. 11 peter iii:7, 10.