On Prayer and the Contemplative Life

A virtue is that which both renders its possessor, as also his work, good. Hence we must say that every good act comes under virtue. And it is clear that to render to another what is his due has the character of a good act; for by the fact that a man renders to another his due there is established a certain fitting proportion and order between them. But order comes under the ratio of good, just as do measure and species, as S. Augustine establishes.