Rabanus Maurus
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.
There are four sorts of trees; the first totally withered, to which the Pagans may be likened; the second, green but unfruitful, as the hypocrites; the third, green and fruitful, but poisonous, such are heretics; the fourth, green and bringing forth good fruit, to which are like the good Catholics.