I have been accused of being dogmatically committed to agnosticism concerning the historicity of Jesus, which I do not believe to be true. What I do believe is that a convincing argument for the existence of Jesus isn't going to depend on our ability to prove the meaning of a single uncorroborated verse in Paul that we cannot prove he wrote anyway. The kind of argument that might convince me is one that explains some broadly observable phenomenon in early Christianity.
One such phenomenon is the way that Jesus becomes less human and more supernatural in the gospels as time goes by. In the earliest gospel, Jesus gets angry and despairs of his fate while in the later gospels he faces his fate with superhuman calm. Perhaps it is reasonable to extrapolate backwards to the earliest figure in the oral tradition being entirely human.
Another idea occurred to me in considering Paul's message in the first two chapters of his letter to the Galatians, which seems mostly to be "Don't listen to those guys in Jerusalem. Listen to me."
Among the things Paul tells the Galatians are are:
(1) My message came directly from God, not from the Jerusalem crowd;
(2) They added nothing to my message;
(3) I ignored them for three years;
(4) Then I ignored them for another fourteen (eleven?) years;
(5) They spy on us and make us slaves;
(6) They are hypocrites;
(7) Their reputations mean nothing;
(8) They agree that it’s my responsibility to preach to the gentiles.
So the question occurred to me: Why doesn’t Paul just ditch these guys? If they are just making Paul’s life difficult, why not just denounce them as false brothers with a false revelation and tell the Galatians to have nothing to do with them. He seems to be doing fine without them and he is clearly unhappy about them interfering in his communities. If this is just a mystery cult based on visions of a purely spiritual being, I wouldn’t think that would be very hard to do.
On the other hand, if the visions were supposed to involve the resurrection of a known human being, then it might be very difficult for Paul to question the authenticity of their experiences without calling into question the authenticity of his own. That might explain why he is forced to acknowledge them as his predecessors even though he denies that they contributed anything to his message.