Great question. The most obvious point is that the Jews and those of a Greco-Roman culture antedate Christianity. Hence, when Christianity came into being, many Jews, Greek and Roman embraced Christianity, but they also brought in their past beliefs and practices. So, there was borrowing and influence. Let me give a few examples. First, the Jewish bible became the basis of the Christian bible. This point cannot be minimized. Second, Greek philosophy was imported into the church in many ways. There is very strong platonic strand of thought within Christianity. The same can be said of Aristotle's thoughts. Third, keep in mind that many of the leaders of the early church - like Paul - were people who were steeped in the world of Judaism and Rome. Paul was a Jewish Roman citizen, who became a Christian.