I like to make sure that I'm believable. If I don't believe me, then there's a lot of people that don't believe me, but if I can believe that I'm doing it, then I know the audience will, too.
The moral law is a reason to think of God as plausible - not just a God who sets the universe in motion but a God who cares about human beings, because we seem uniquely amongst creatures on the planet to have this far-developed sense of morality.