St. Thomas understands the good- whether moral or transcendental- as an act, which means it must be understood as the perfection of some potency. A failure to divide being into act and potency, therefore, will lead to a denial of the reality of goodness. For example, a failure to see the reality of potency requires positing an insurmountable distinction between “the is and the ought”, for ought is said first of potency. If nothing is potential, nothing is perfectible, and if nothing is perfectible, we lose our first notion of perfection. Moreover, without some idea of potency the transcendental good simply never comes up.
Even otherwise very profound thinkers say the stupidest or awkward things about goodness if they do not see the reality of potential being. Max Scheler, or example, said Aquinas thought all being was good because he was rich and had money, and Anscombe’s account of Aristotle’s ethics is often awkward because it totally overlooks Aristotle’s teaching on the reality of potency, which is the foundation of all goodness- moral or otherwise.
For Aristotle and St. Thomas, the question of moral goodness or “the ought” is a particular application of the universal distinction of potency and act. One must understand how being as such is good before understanding the foundation of how a human being or human action in particular is good. Ethics in St. Thomas and Aristotle is founded on the realization that all goodness is what perfects in the mode of an end, and so goodness must correspond to something that needs to be or ought to be perfected (a potency). In moral questions the potency in one sense is a man, in another more precise sense it is a man’s appetites. These appetites are perfected in one sense by their objects, an another sense by actions, in another sense by habits of choosing. There is a great deal that can be fleshed out here, but without seeing the reality of potency the whole project of virtue ethics (and even ethics as such) will never get off the ground.