I hesitate to use any of my limited knowledge of the sciences here, because I am sure other people know more and better. but at some point a chemical reaction happens "just because". You mix two elements and a imbalance of ions will lead to chemical reactions. the ions are that way because of their electrons. their electrons are that way because of pairing and orbit. the orbit and pairing happen because of balance. why the balance? again someone here probably knows and can correct what I said. but even if you take it a couple steps down to the quantum level, its just because.
this also falls short because its "just because" for now, until we have a better understanding of the subject. in the case of God you have limited your experience/learning of him, so you come across just because a little sooner than others. Not saying I, or anyone, has a better final answer than "just because", but I have no problem accepting that with God when I do the same with things beyond my comprehension.
the Golden Rule, which it sounds like you subscribe to, boils down to just because. or in actuality, it boils down to selfishness. I do this so that someone else will do this to/for me. but why? Karma, destiny, cosmic balance? Or at some point is it just because? its right? why? just because you have a selfish belief that it comes back around, potentially? Right is right? but God can't be God? and he can't be, because its an arbitrary explanation, just like right is right because it serves my purpose?