It may be because so many modern aggressive atheists are from a science background that they fail to understand the way in which historians proceed; but quite what excuses their ignorance when this is pointed out is a matter for their care workers and not for me.
The notion that people who had seen their beloved leader die on the Cross would, in some ay not explained, all collude in a delusion that He had risen from the dead is simply a form of atheist madness. No one has delineated such a mass delusion across even a decade, let alone centuries; yet atheists who pride themselves of their devotion to reason can trot out the idea of mass delusion without blushing. Paul knew that eye-witness testimony mattered, and as he told the Corinthians, more than five hundred people has witnessed the Risen Lord; he offered important names among them. Paul was more than happy for contemporaries to check his story out. The same was true of Luke, who puts at the very start of his Gospel the declaration that it is based on eye-witness testimony; St. John’s first Epistle does the same. These men had seen what they preached and happy to call in aid eye-witness testimony. If modern atheists wish to behave like the bad part of doubting Thomas, that’s their look-out, but to say there is no eye-witness testimony is simply incorrect. There’s more and better corroborated testimony for Christ’s resurrection than there is for Caesar landing in Britain.
Paul called on that testimony because of who he was. An avowed enemy and persecutor of the Christians, he was received by them with some suspicion, and the notion that such a man could simply come in with his fancy ways and rewrite what others had seen and what he had not is, again, one which carried weight only in atheism 101, that fact-free zone where atheists cheer each other up by repeating improbable stories and then attributing them to Christians. Paul came as a penitent to the Church, one with an important vision, but there was nothing in that vision which was not already known to those to whom he talked. The fact was that Paul needed to be vetted and checked out, and he was. His vision matched what the early Christians already knew – that was why they accepted Paul.
But Paul never occupied any leadership position in the Church in Jerusalem – indeed he paid an enormous personal price for his conversion. His old allies, the Pharisees, pursued him with hatred to his death, and it is clear that James the Just and the official leadership regarded Paul and some of his ideas with lasting suspicion. If we stand back a moment we will see that Paul spent his life as an itinerant missionary, suffering many hardships, including shipwreck and persecution, and indeed, ended by receiving martyrdom in Rome under Nero.
If we place Paul into his context, we see, even before we examine any detailed evidence, how improbable it is that he would have been able to come in with a very different version of what Christ taught and who He was – let alone have been able to convert to such a view those who had seen the Lord in the flesh.