Let's say there really was a Jesus. He was born out of wedlock and his father explained to him, to save him embarassment, that he never had sex with his mother, that it was some kind of miracle. Okay, now JC grows to be a lad and gets caught up in the phony baloney explanation his old man gave him.
Now his friends who have been making fun of him for being a bastard decide to let it be and just get along with him. Unable to let go of the stigma of being born out of wedlock, JC becomes maniacal about his 'miraculous' conception and really begins to believe it himself. He sets out as a young man looking for someone who will believe his malarky and happens upon a group of incredulous young men like himself that wish to eat this story whole.
As the tale grows in the telling he lets it be known that he is destined to become a god on earth. He convinces his friends that he can perform miracles himself but no one else gives him even a mention in the local papers, as they realize he is full of it and is worthy of no notice.
Push comes to shove with his followers and JC is forced to declare even bigger statements involving his link with 'god'.
In his own dillusion he decides to have himself crucified, claiming he will come back after being dead. Its an easy thing to do, (getting nailed up), all he has to do is piss off the local establishment and away he goes.
He is bolted to the cross, appears to die, his buddies pull him down and go through a mock burial in a cave. Three days later, the never dead dude makes his miraculous recovery and the rest is history!
Sound plausible?