Jerome
Catena Aurea · Matthäusevangelium 7
Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits ye shall know them.
We would ask those heretics who affirm that there are two natures directly opposed to each other, if they admit that a good tree cannot bring forth evil fruit, how it was possible for Moses, a good tree, to sin as he did at the water of contradiction? Or for Peter to deny his Lord in the Passion, saying, I know not the man? Or how, on the other hand, could Moses’ father-in-law, an evil tree, inasmuch as he believed not in the God of Israel, give good counsel?