Voltaire (or someone else) thought God to be the Prime Mover. I can't recall undergrad philosophy well enough to say if he was religious by our current definition.
Why can't it be a physical force then? Makes a lot more sense. Except that it's not comforting idea, it forces to realize that in that case life has no purpose and no goal, no meaning for the suffering of many, no reason, no nothing, just an endless happening. That's why people insist on a "god" idea, that's the only reason, otherwise a physical force as a "god" is a lot more reasonable explanation however you look at it.