Speaking as a Christian I've always simply assumed that God, being God, isn't obligated to obey human morals and values simply because the Godhead is not human. God can no more obey our values or conception of morality than we can obey His conception of morality and His values. For example: if you assume God exists, as I do, how can you even begin to think upon how an infinitely intelligent entity (as God is generally consider to be) thinks, draws conclusions/makes decisions, solves problems, etc.? You can't and all you're left with is a non-sequitur. The closest comparison that I can think of is in the case of ETs. If ETs have a different moral values system than humans then how can we really expect them to understand or grasp ours? Quite a brain-tickler.
There's more than a few passages in the Bible that make it quite clear that, while morality exists, God's morality is not human morality, that God's way of thinking is not the human way of thinking, etc.
'For My thoughts are not your thoughts: nor your ways my ways, saith the Lord.' (Isaiah 55:8)
I believe Plato and his school wrestled with the idea of a source of transcendent moral order well before the emergence of Christianity and Plato's conclusions were much the same as the Christian perspective (due in no small part from copious borrowing from the Platonist by the Christians): the reason that morality exists and is therefore true is because the source of morality is, itself, of a non-human origin and is one and the same as the Creative Principle (or God). Or something like that. I haven't read from Plato's writings in a while. Cheers.