The Impossible Moral Epistemology

Let's say, hypothetically, that a form of divine command theory is true. That the only ontology in which objective morality makes any sense is one grounded by God. Now comes the question of epistemology - how do we know what's good? No matter what premises one puts as the grounding of the ontology, there's simply no way of deriving what is right or wrong. Rather we're left making the subjective judgement based on our own nature, reason, revelation, or perceived authority. And even after all that we're still none the wiser.

There's the problem that we simply cannot recognise what is good as we have no objective way of knowing it. The sacrifice of holding such a moral ontology is the absolute devotion of faith that the morality one is taught or feels a deep inner conviction towards is the morality - just like everyone else. To hold such a moral ontology, to my mind, is giving up any chance at moral knowledge for the sake of necessitating God.