I think that a bunch of fishermen (Jesus and his disciples) were getting high on a field and then one of them called Jesus was like "look I'm walking on water" and the others thought they saw him do it and they were like "it's a miracle" and then they went and told the villagers and they all wrote a book about what the fisherman named Jesus was supposed to have done and his friends, or 'disciples'.
That's what me and my dad came up with one time anyway.
I think that someone, or a group of people, from not long after humans first evolved wrote the basic ideas behind all the relgions down in symbols or the language they used and then it got discovered years later and there was argument over how it is translated, that then lead to the different holy books and then people just believed them as they were looking for an answer.
Or maybe a man called Jesus did something heroic and then the rumours got exageratted as they got passed on into "he walked on water" and "he cured this uncurable disease" etc. and everyone believed it and then he went along with it and told them he was the son of God or his mates did, maybe.
Anyway, there my theories and in case you hadn't guessed I believe in evolution.
Gives people someone to look up to
But, that's just me.
