God's Will Decides Morality

What is done in accordance with God's will is the best of all things even if it seems to be bad. What is done contrary to God's will and decree is the worst and most unlawful of things--even if men judge that it is very good. Suppose someone slays another in accordance with God's will. This slaying is better than any loving-kindness. Let someone spare another and show him great love and kindness against God's decree. To spare the other's life would be more unholy than any slaying. For it is God's will and not the nature of things that makes the same actions good or bad. Fathers of the Church (vol. 68), St. John Chrysostom, Discourses Against Judaizing Christians, translated by Paul W. Harkins, Discourse IV, section I, paragraph 6 (p. 74)