Upon whether there is a God or not.
stands2reason: Upon whether there is a God or not.
Good answer. But wouldn't it be more accurate to say that it's based upon whether G-d Himself is moral? Or, more clearly, that G-d has declared what is right and what is wrong, and by His moral character has shown Himself to be a valid source?
I would propose that the entire story of Adam and Eve and the Fruit of the Tree of the Knowledge of Good and Evil is about just this question. Is morality something that man can know on his own? Has he the ability to know all possible ramifications of a decision to know whether it will result in good or evil? Can he, as Gandalf suggested, know all ends? Or is he dependent on a good, all-knowing Creator to tell him what is good and what is evil?
By eating of the fruit, Adam and Eve declared they could figure it out for themselves. G-d allowed them to make that choice, and in so doing they destroyed paradise.
But I believe this to be true because I believe G-d exists, that G-d created this universe and all that is in it, and that the Bible tells the story of G-d's relationship to Man.
If G-d does not exist, if G-d did not create this universe, if it is all an accident, then there is no morality. In that case, the Bible is an interesting book, but no more able to help us know how we should treat each other than our gut instincts.
This is why I say "If man is an accident then it doesn't matter how we treat each other."
I hope I have been clear about what I believe.
Shalom.