Here is an excellent article from Graham Veale of Saints and Skeptics on the existence of Jesus. There is no doubt that the historical figure known as Jesus existed and is not part of a pagan myth as some people claim.
You can read the article here:
We know beyond any doubt: Jesus Existed | Saints and Sceptics
1. It is impossible to explain why Christianity would shift from worshipping a mythical Christ to preaching an historical Christ. Suppose the shift was the result of a deliberate conspiracy. Why would the conspirators open their message to refutation in this way?