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.
Or, I think the thorns and bramble are the cares of the world and the prickings of sin, but the figs and the grapes are the sweetness of a new life and the warmth of love, but the fig is not gathered from the thorns nor the grape from the bramble, because the mind still debased by the habits of the old man may pretend to, but cannot bring forth the fruits of the new man. But we must know, that as the fruitful palm tree is inclosed and supported by a hedge, and the thorn bearing fruit not its own, preserves it for the use of man, so the words and acts of the wicked wherein they serve the good are not done by the wicked themselves, but by the wisdom of God working upon them.