I once saw something on TV where George Lucas was talking about The Force. He said that he was attemping to create a very simple, universal religion for the Jedi. Most religions share the idea that there is something beyond our physical world, and this is where the idea of The Force came from. Also, any religion worth the name has some concept of good & bad, hence the Light Side and Dark Side. As for the special powers that the Force gives, well, that’s because Lucas really really wanted the Jedi to be superpowered ass-kickers 