I would define "Morality" as the wish to maximize pleasantness and minimize unpleasantness in advanced sensing beings that are not causing unnecessary suffering, while avoiding unnecessary suffering.
Moral absolutes in human affairs are determined by human nature. There is just one natural "Way" for humanity to arrange it's environment and interactions to achieve maximum pleasantness.
If God is necessary to generating and sustaining that Way, The Deity is necessary to Morality.