Is there a denomination or Christian religion that believes that Jesus Christ was just an idea or way of thinking and that the apostles must have personalized him for the people to understand it easier? If so, what is their biblical basis for rejecting the historical personhood of Jesus? I'm not asking on the historicity of Christ.
Mark 6:45-56 Shortly before dawn he went out to them, walking on the lake. He was about to pass by them, but when they saw him walking on the lake, they thought he was a ghost.
He was about to pass by them? It doesn't make sense. It would make sense if he was going towards them. This is something that could be taken as a metaphor from the Old testament. Title for God, the one who walks on water. Job 9:8, Psalms 76:19, LXX]
Further arguments would be that the whole life of Christ could be summed up into something that the first Christians started to believe. That is was their new way of thinking and that surrounding Jews tried to kill this new way of thinking but in 3 days it rose again.