Why is there a big difference between religion?

Because there are different gods in every religion

Well, for one, every single religion is different. Even though, they may have some of the same beliefs, they are still different. For instance, Catholicism and Christianity. They both worship the same God. Catholics, however, believe in worshiping Mary like she was a saint. They also have a thing that they do after prayer. Children get christened right after birth, etc. Christianity, however, doesn't practice any of the things I just mentioned.