Augustine of Hippo
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.
(Serm. in Mont. ii. 24.) Wherefore it is justly asked, what fruits then He would have us look to? For many esteem among fruits some things which pertain to the sheep’s clothing, and in this manner are deceived concerning wolves. For they practise fasting, almsgiving, or praying, which they display before men, seeking to please those to whom these things seem difficult. These then are not the fruits by which He teaches us to discern them. Those deeds which are done with good intention, are the proper fleece of the sheep itself, such as are done with bad intention, or in error, are nothing else than a clothing of wolves; but the sheep ought not to hate their own clothing because it is often used to hide wolves. What then are the fruits by which we may know an evil tree? The Apostle says, The works of the flesh are manifest, which are, fornication, uncleanness, &c. (Gal. 5:19.) And which are they by which we may know a good tree? The same Apostle teaches, saying, The fruits of the Spirit are love, joy, peace.