Why do people believe in god?

How is anything like that possible? A "spirit"? It's just like saying ghosts are real. Christianity and Catholicism are pretty dumb religions. Anyone could have written the "Holy" Bible how ever they wanted it. Like the whole thing about the 'Earth is the center of the universe' thing, the churches taught that... And don't give me some dumb answer like, "You have to be faithful"- why would I have faith in something that is just theory? In fact, why are there any religions at all?