This is actually something I have given a lot of thought to and so I think I have an answer, but I’m not sure if it’s exactly the answer you’re looking for. But the basic idea is that moral authority necessarily follows from omnscience which necessarily follows from omnipotence.
Consider this model, whereby the universe can be represented as a series of choices represented in a tree-like structure and each choice has a certain degree of moral relevance. We can relate this model to sort of a massively multiplayer game theory, but we can simplify it to something more easily conceptualized like chess. Sometimes, a particular move in chess is obviously superior to others, sometimes its a lot more subtle or even counter-intuitive, but the only way to be absolutely certain that a particular move is optimal is to actually build the entire space and evaluate it from a min-max perspective.
Now, obviously, as humans, we’re not able build out the entire state-space for chess, but we can still look some number of moves ahead and build rules that help us determine what states are more or less advantageous toward furthering the ultimate goal. These rules are akin to moral rules in this analogy. But God, being omniscient, would be like actually being able to see and evaluate the entire state-space and give the absolute optimal move which will likely often fit along with the rules but will occassionally not fit them for some reason or another.
And so, this would be like seeing this space and evaluating certain generalized scenarios from different states and drawing general rules. Just like a beginning player will have broader rules that roughly fit more scenarios but work less often and a more advanced player will have a larger set of more specialized rules, morality works in much the same way. We’re in the process of traversing this massive state space that we can’t possibly fathom, so we have to stick to certain guidelines that will best lead us toward the goal. As we, as a species, have gotten more developed, our ability to understand the rules, and thus our ultimate understanding of them, has improved. But this entire time, being omniscient and omnipotent, God is able to observe the entirety of the choices and their consequences and provide us with guidelines toward the goal.
Of course, this leaves one question where the analogy doesn’t work as well, in that in game theory there’s an obvious goal to work toward, winning; there isn’t something as obvious with morality. Some might try to say something like “best for the most people” or “happiness” but those are sort of nebulous goals that don’t quantify them. I have my own thoughts on what that goal may actually be, that, in fact, choice isn’t merely a means to an end but is an end in and of itself but I haven’t really managed to flesh that aspect out sufficiently yet.
So, in the end, it all boils down to that omniscience which derives from omnipotence, that if you can necessarily see all the possible outcomes for every possible decision and make a judgment about which one yields the best possible set of results, then it seems to me that moral authority naturally follows from that.
