For once I actually agree with atheists and agnostics. It is relatively easy to make up a story about a dude that does not exist and make him fulfill prophecies. EVEN assuming that he did exist, which is questionable, he didn't shake the Empire to its core. Christianity had very little effect on the Empire for a couple of centuries, and by the time it did, it was a far cry from what Jesus had taught, having embraced so much doctrine from the Eastern Mystery Cults.
KMAN, that gets into a very interesting topic. Occasionally, G-d has altered laws to apply to Jews that did not previously apply to people generally. For example: People generally were allowed to eat only herbs when he created people. Then they were allowed to herbs and meat when he gave laws to Noah. Then the Torah was given the Hebrews that gave us our unique set of dietary laws that affect only us.
Its hard to explain to you in this medium. But, another example is the following:
According the Jewish tradition, Abraham gave us Morning Prayer. Isaac gave us Noon Prayer. Jacob gave us Evening Prayer. During the respective life of each Patriarch, we prayed once a day, twice a day, and eventually thrice a day, and before that, we prayed only privately and individually rather than corporately.
I don't know if that helps get my point across. But in this medium it is hard to discuss logically.