I've had an interesting thread going on over at the Christian Fools board:

http://boards.fool.com/Message.asp?mid=24816703

I was curious about what mitzvot Christians follow. Obviously they don't follow most of them (kashrut, shabbat, taharat hamishpacha, shatnez, etc. etc.), but obviously they do follow some (against murder, sexual immorality, and (though some Jews would disagree) against idolatry.

Anyway, one of the messages concerned Paul of Tarsus. If you don't know who he is, you can learn about him here:
http://en.wikipedia.org/wiki/Paul_of_Tarsus

The Christian version of Paul's story (as I understand it):
Originally named Saul, he was an anti-Christian activist. He was sent by the Sanhedrin to Damascus to arrest Jewish followers of Jesus. (At this time, Christianity was still a sect entirely within Judaism.) On the way, he had a vision, became a Christian himself, and changed his name to Paul. He became a Christian leader, and declared that brit milah was no longer necessary for converts to Christian Judaism. (He did away with most of the other mitzvot as well.)

The practical result was that lots of non-Jews became Christians (get saved, quick & easy! No muss, no fuss!), while many of the Jews who had believed in Jesus as Moshiach became disaffected with the movement. Belief in Jesus lost all traction within the Jewish community.

I once heard a lecture in which the theory was put forward that Saul invented the whole thing. In this theory, the only vision he had on the road to Damascus was the plan he formulated to make Christianity repulsive to Jews. He would become an agent provocateur. He was sent by the Sanhedrin to put a stop to this new sect within Judaism, and with his made up story of a vision and conversion, that's exactly what he did. He told people they could substitute belief in Jesus for observance of mitzvot. By making Christianity a new religion that was incompatible with Torah Judaism, he drove the Jews away from the sect.

i wish I could provide more detail, but I heard the lecture over 20 years ago. I heard it at Yeshivat Ohr Somayach, but the speaker was a guest-lecturer from Aish Hatorah.