You mention a few reasons for Christianity’s quick growth: eternal life, human Jesus, open to all. But what about tax incentives? There was a fiscus ludaicus tax on all Jews. The early Jewish-Christians were exempted by emperor Nerva and this head tax wasn’t abolished until 2-3rd century.
I think I read somewhere that Muhammad started Islam as a tax dodge? This can be seen with jizya tax on non-Muslim citizens.
And how about this theory that Jesus and Judas the Galilean are the same? Josephus really only wrote of Jesus death and Judas temple cleansing.
Any suggestions of books on ancient taxation?