Worldviews need to be consistent, both at a theoretical and practical level. Now, here is an alleged worry for theism. It aims to infer its practical inconsistency. On theism God is the ultimate origin and sustainer of reality. As such God is a sacred or holy being of maximal worth and praiseworthiness. But then, if God commands a human creature to perform some action, he or she seems obliged to obey.
Yet, what if God commands John to perform a morally despicable act, say killing his own newborn son? Would John have to obey? If so, theism seems to be in conflict with our deepest moral convictions, rendering the theistic worldview practically contradictory.
How should the theist respond? One may contend that there are good arguments for the claim that it is metaphysically impossible for God to command morally despicable acts. For God is understood to be a maximally perfect and thus a necessarily good being. So God simply cannot order John or others to perform morally blameworthy acts.
This response has a slight disadvantage though. It requires the theist to be committed to the substantive claim that it is metaphysically necessary that God is good, while not all theists accept this. Some, such as Richard Swinburne, maintain that it is a brute fact that God is good. That is to say, God is in fact good but not necessarily so.
One could simply say that although God is perhaps not good in all possible worlds, still in the actual world God in fact does not ask people to perform morally despicable acts. So in the actual world commands to be cruel do not originate from God. But how does the theist know this? If God is not understood to be metaphysically necessarily good, for all we know God may command us to be morally cruel. The theist needs a convincing reason for believing that in the actual world God refrains from commanding moral despicable acts, so that John doesn't have to obey. But if God’s necessary goodness isn’t presupposed, it seems problematic to obtain such a reason.
Let me therefore suggest another way to respond to the worry. If John is ordered to kill his own newborn son by some being, it is metaphysically impossible for John to know with sufficient certainty that the being in question is in fact God. It is not that John has to be committed to God’s necessary goodness or to God not commanding morally despicable acts in the actual world. John may leave these matters entirely undecided. It’s just that John cannot know surely enough that a being who commands him to perform such a morally despicable act is indeed God. That’s why he shouldn’t obey, without by doing so jeopardizing God’s majesty.