Keep in mind, Christianity did not spread via military conquest, as did Islam. Becoming a Christian meant 1) accepting that a God had become a man—something completely counter cultural—and then 2) serving others at great sacrifice to oneself.
Anyone today who rejects the New Testament must explain how the church “exploded” at the beginning of the first century, ultimately and peaceably “conquering” the Roman Empire that tried to extinguish it and, in so doing, changing the course of the entire world’s history.
As German historian Martin Dibelius says, “You have to posit an X big enough to explain the Y of the early church.”