St. Augustine on Good Fruits

 As long, therefore, as any one is evil, he cannot bring forth good fruits; for if he were to bring forth good fruits, he would no longer be evil. So it might most truly have been said, snow cannot be warm; for when it begins to be warm, we no longer call it snow, but water. It may therefore come about, that what was snow is no longer so; but it cannot happen that snow should be warm. So it may come about, that he who was evil is no longer evil; it cannot, however, happen that an evil man should do good. And although he is sometimes useful, this is not the man’s own doing; but it is done through him, in virtue of the arrangements of divine providence…

St. Augustine of Hippo, Sermon on the Mount XXIV.79