The rise of Christianity is a great puzzle. In 40 AD, there were maybe a thousand Christians. Their Messiah had just been executed, and they were on the wrong side of an intercontinental empire that had crushed all previous foes. By 400, there were forty million, and they were set to dominate the next millennium of Western history.
Imagine taking a time machine to the year 2300 AD, and everyone is Scientologist. The United States is >99% Scientologist. So is Latin America and most of Europe. The Middle East follows some heretical pseudo-Scientology that thinks L Ron Hubbard was a great prophet, but maybe not the greatest prophet.
This can only begin to capture how surprised the early Imperial Romans would be to learn of the triumph of Christianity. At least Scientology has a lot of money and a cut-throat recruitment arm! At least they fight back when you persecute them! At least they seem to be in the game!