Bede the Venerable
Catena Aurea · Lukasevangelium 6
For a good tree bringeth not forth corrupt fruit; neither doth a corrupt tree bring forth good fruit. For every tree is known by his own fruit. For of thorns men do not gather figs, nor of a bramble bush gather they grapes. A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh.
The treasure of the heart is the same as the root of the tree. He therefore who has in his heart the treasure of patience and perfect love, brings forth the best fruits, loving his enemy, and doing the other things which have been taught above. But he who keeps a bad treasure in his heart does the contrary to this.