Christianity was spread person to person...
...as a dynamic faith delivered verbally, empirically.
The four Gospels were Midrash or homiletic sermons that were eventually written down...
...and the rest of the New Testament documents were letters sent to remote communities addressing specific local issues.
Christianity is not sustained/maintained by these documents...
...or by the witness of extra-biblical historians...
...Christian Apologetics is not evidence of faith but unfaith.
Christianity is the personal realization of the historicity of the resurrection confirmed directly, individually by the Spirit...
...and the ongoing dynamic personal relationship that follows.
You will never understand Christianity until you understand that historical documents are no more the basis of a Christian's faith relationship than
the existence of a marriage certificate is evidence of a successful marriage.