I don't know about the shrooms, my reading of the old testament made me think it started with some old guy trying to stop his nomadic desert tribe dying of anything too stupid by telling camp fire stories with some sort of message. The whole 'god will make the ground open up to swallow you and your family if you screw up' is a desperate attempt to scare them into not doing stupid things like slaughtering too many of their livestock at once, or eating shellfish whilst wandering around in a desert.
The stories get retold, changed and embellished over generations before being written down, and you end up with the weird mess of basic survival tips, animal husbandry, heroic stories and mystic fluff that is the OT.
The new testament is just the story of a fairly chill guy, with a slight messianic complex, wandering around with his mates and suggesting people be nice to each other, put through a similar transformation.