C.S. Lewis gives a good answer to essentially this question in God In The Dock: Essays on Theology and Ethics.
I can’t say for certain which bits came into Christianity from earlier religions. An enormous amount did. I should find it hard to believe Christianity if that were not so. I couldn’t believe that nine hundred and ninety-nine religions were completely false and the remaining one true. In reality, Christianity is primarily the fulfillment of the Jewish religion, but also the fulfillment of what was vaguely hinted in all the religions at their best. What was vaguely seen in them all comes into focus in Christianity – just as God Himself comes into focus by becoming a Man.
One observation often made is that Continue reading “Didn’t Christianity just copy from earlier religions?”