With considerable rapidity, therefore, Greek mythology, Greek philosophy, and Oriental cults were being accommodated to one another, and brought together in a new and highly complex religious system. For political purposes the introduction into this system of the worship of the emperors, living or dead, was of great importance. It tended to unify the whole mass, and the imperial authorities adopted the position, with some reservations, that, provided a man accepted the cult of Caesar and Rome, he could in addition be a member of any other religion which pleased his fancy or soothed his soul.

There was one exception to the ease with which the Oriental cults accepted the situation. Still inspired by the instinct which nine hundred years before had made their prophets fight against syncretism, the Jews resolutely refused to come to terms with heathen religions. Some, indeed, accepted the Greek philosophy, as the writings of Philo and the Wisdom Literature show; but with the cults or with the mythology of the heathen no compromise was tolerated.

It would be interesting to know how far the imperial leaders perceived the process of synthesis, but consciously or unconsciously they helped it considerably by the policy which they adopted towards the local councils, or Synedria—Sanhedrims—as they were often called.[[2]] They were willing to encourage their continuance, allowing them to control all local questions of religion, and indeed all local interests generally, on condition that they made themselves also responsible for the cult of Rome and of Caesar. In this way Caesar was introduced into the local religion, and, what was much more important, the local religion was absorbed into the unified system of the Empire. The policy was almost uniformly successful: the one exception was the Sanhedrim of the Jews, which obstinately refused the imperial cult and resisted Caligula's effort to introduce his statue with the same successful pertinacity as had repelled the efforts of Antiochus Epiphanes in the days of the Maccabees. The episode ended disastrously, for the spirit of nationalism and unreasoning hate to the government of Rome roused a rebellion which inevitably led to the fall of Jerusalem and the violent destruction of Jewish national life. Henceforward the official Jewish religion remained a foreign element in the life of the western world. It could not die, for in spite of rabbinical extravagances it possessed more ethical truth than heathenism, and was more sincere in its protest against superstition. But neither could it form a synthesis with the better elements of the Roman world; the process of accommodation to Greek philosophy was stopped for many centuries, and the Jew had neither part nor lot in the life of the empire in which necessity compelled him to live.

Nevertheless in the end the inevitable synthesis between Judaism and Greek thought was accomplished, though the official world was unable to bring it about. The small and at first despised sect of Christians was driven out of the Synagogue and forced into contact with the heathen world, at first probably against its will. There is nothing to show that Christians originally desired to break away from Judaism or to approach the Greeks; yet they did both. When their fellow-countrymen refused to hear they turned to the Gentiles, and there ensued rapidly the abandonment of Jewish practice and the assimilation of Greek and Graeco-Oriental thought.

From that time on the history of Christianity might be written as a series of syntheses with the thought and practice of the Roman world, beginning with the circumference and moving to the centre. The first element which was absorbed was the least Roman, the Graeco-Oriental cults. Christianity had been originally the worship of God, as he was understood by the Jews, combined with the belief that Jesus was he whom God had appointed, or would appoint, as his representative at the day of judgement. To this were now joined the longings for private salvation of the less fortunate classes in the Roman Empire, and their belief that this salvation could come from sacraments instituted by a Lord who was either divine by nature or had attained apotheosis. It thus became, partly indeed, the recognition of the Jewish God as supreme, but chiefly the recognition of Jesus as the divine Lord who had instituted saving mysteries for those who accepted him. Christianity became the Jewish contribution to the Oriental cults, offering, as the Synagogue never did, private salvation by supernatural means to all who were willing to accept it.

Such Christianity became, and such in some districts, notably in Rome, it remained for one or two generations. But in Ephesus and possibly elsewhere a further synthesis was accomplished. This sacramentalised Christianity began to come to terms with Greek philosophy, as the other mystery religions tried to do. It asked what was the philosophic explanation of its Lord, and it hit on the device of identifying him with the Logos—a phrase common to several types of philosophy though used in quite different meanings.

The development of this second synthesis was comparatively slow. Probably some of the systems which are loosely described as gnostic were unsuccessful attempts at its accomplishment; but in the end the Alexandrian theologians Clement and Origen followed the lead given them by the Fourth Gospel and some of the apologists to the triumphant construction of a system which really reconciled in part and seemed to reconcile entirely the Christian cult and the later Platonic metaphysics.

Although the general fabric of the Christian philosophy which was thus built up was in the main Platonic, not a little was borrowed also from the system of the Stoics, especially on the border ground between metaphysics and ethics. This paved the way for a further synthesis, accomplished more easily, more thoroughly, and with less perceptible controversy than had attended either of the others. Probably the culmination of this conquest of the Christian Church by the ethics of the Stoa was reached by Ambrose, who gave to the Christian world Cicero's popularisation of Panaetius and Posidonius in a series of sermons which extracted the ethics of Rome from the scriptures of the Christians. The ethics of the Stoics were almost wholly adopted by the leaders of Christian thought, especially in the West, and the teaching of Jesus as represented in the Gospels was interpreted in the interests of this achievement, which, like the other syntheses, was largely effective in proportion as it was unconscious.

Probably it was the early stages of this movement which had rendered possible the acceptance by one another of Christianity and the Empire. Certainly there is still much need of study, even if it produce only the statement of problems, as to the changed character of Christianity between the time of Tertullian and Eusebius.

The next few centuries, so far as they were not occupied in struggling against the eclipse of civilisation which began in the fifth century, were occupied in working out the implications of these syntheses. The results were codified in Catholic theology and in the civil and canon law of the early Middle Ages. But one more step remained; after nearly a thousand years Aristotle was rediscovered, and the final achievement of Christian theology was the synthesis effected by St. Thomas Aquinas between the Christian theology and the philosophy of Aristotle.