Because Abrahamic faiths think that their the only one religion so anything else isn't real. So we say don't mess with that kind of stuff because you don't know what kind of spirits can behind that kind of stuff.
Calvin is wrong. No one forced me to love God, I did it on my own behave. The whole idea of everything is predestined destroys the whole concept of why God created us in the first place.
Good for you mate! I'm glad God opened open a path in your life to those self motivations class's or books etc. I'm glad your not a bum, but your actually doing something with your life.