Religion

Paul claimed the holy poltergeist whispered into his ear at a low moment in his life (I'm thinking at the end of a wine bender) and told him exactly what to do.

The reason Christianity had to depart from Judaism centered around the subject of circumcision. The problem Paul had was Mosaic law required Jewish men to be circumcised. Circumcision during a time of no sterilization of tools and no antibiotics was a risky proposition. It was one thing to do it to babies that had a high mortality rate anyway. It was quite another to volunteer for the process as an adult when you stood a good chance of pieces falling off or worse. In order to bring the rich Romans and Greeks to the party, Paul knew he had to change the law. There was quite a bit of division in the early church over the subject.

So it really wasn't all that crazy. Just the workings of a religious huckster who was better at his craft than most.