Gregory the Great
Catena Aurea · Matthäusevangelium 3
But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come? Bring forth therefore fruits meet for repentance: And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham. And now also the axe is laid unto the root of the trees: therefore every tree which bringeth not forth good fruit is hewn down, and cast into the fire.
(Hom. in Ev. xx. 8.) Observe, he says not merely fruits of repentance, but fruits meet for repentance. For he who has never fallen into things unlawful, is of right allowed the use of all things lawful; but if any hath fallen into sin, he ought so far to put away from him even things lawful, as far as he is conscious of having used unlawful things. It is left then to such man’s conscience to seek so much the greater gains of good works by repentance, the greater loss he has brought on himself by sin. The Jews who gloried in their race, would not own themselves sinners because they were Abraham’s seed. Say not among yourselves we are Abraham’s seed.