To move from Greek philosophy to the first four centuries of Christian thought is to introduce a large new subject. But we would leave a serious gap in an account of Greek philosophy if we said nothing about Christianity. The formation of Christian thought was influenced from the beginning by Greek philosophy. Some of the Jewish scriptures, and especially some of the Apocryphal works, are affected by Stoicism; and Philo's (c. 20 BCc. AD 50) attempt to explain Jewish religion in Platonist terms began a Christian tradition.

It would not have been easy to predict the mutual influence of Christian faith and Greek philosophy. Saint Paul is quite defiant:

For the Jews ask for a sign, and the Greeks inquire after wisdom, but we proclaim Christ crucified, a cause of offence for Jews, and a piece of foolishness to Gentiles, but for those who are called, both Jews and Greeks, God's power and God's wisdom.

Many Greeks agreed with his account of their attitude; but he suggests that their impression of Christianity is superficial. Similarly, Christ claims continuity with the ethical traditions familiar to his audience: 'Do not suppose that I came to abolish the law and the prophets; I did not come to abolish them, but to complete them.' Christians eventually agreed that his claim to complete human traditions was true not only of the Jewish law and prophets, but of Greek rational inquiry as well.

In the three centuries after the writing of the New Testament the Church was forced to decide between conflicting interpretations of the faith that Christ and the Apostles had taught; and Christian theologians turned to Greek philosophy, especially to later Platonism, to answer questions about God and Christ that had been left without explicit answers in the Scriptures. Some of the answers were embodied in the Creeds and the decisions of the oecumenical councils.

Though at first it was philosophy that influenced Christianity, the influence later ran in the other direction as well. Even when it used Greek philosophy as a means of self-expression, Christianity challenged some of its most widely shared assumptions. Both the topics of philosophical discussion and the range of answers to be taken seriously were affected by the claims of faith. There have always been some Christians deploring the alleged 'Hellenization' of Christianity. The protest of the heretic Tertullian (c. 160-c. 225) has also received orthodox support:

What indeed has Athens to do with Jerusalem? What has the Academy to do with the Church? What have heretics to do with Christians? . . . Away with all attempts to produce a Stoic, Platonic, and dialectical Christianity.

On the other hand, there have been philosophers distrusting the influence of dogmatic Christianity on philosophy, indeed on rational inquiry generally. The Christian apologist Origen (c. 185c. 254) thinks it important to answer the attack of the pagan Celsus, who complains about Christians:

Such is the effect of the faith which has prejudiced their minds . . . They show that they want and are able to convince only the foolish, dishonourable, and stupid, and only slaves, women, and little children.

Origen regards this charge as a misrepresentation of Christianity, and his attitude became the orthodox view of Christian faith and Greek philosophy. But it never seemed obvious that the two outlooks could be reconciled.