Society and culture are a shared mythology, without it you have a bunch of people doing their own thing but no real direction. Regions typically generated their own mythologies because of shared hardships. Religions typically co-oped those existing mythologies (though not always, genocide was used too) into their beliefs in order to more easily convert masses of fresh bodies.

Successful religions typically have a few meta-memes built in. "Have kids or get punished". "Teach those kids your religion or get punished". "Tell other people to join your religion" "If those other people don't want to join your religion turn them into fertilizer".

It's a very good way to spread a shared myth.