For a good tree brings not forth corrupt fruit; neither does a corrupt tree bring forth good fruit.
Read Chapter 6
Ambrose of Milan
On the thorns of this world the fig cannot be found, which as being better in its second fruit, is well fitted to be a similitude of the resurrection. Either because, as you read, The fig trees have put forth their green figs, that is, the unripe and worthless fruit came first in the Synagogue. Or because our life is imperfect in the flesh, perfect in the resurrection, and therefore we ought to cast far from us worldly cares, which eat into the mind and scorch up the soul, that by diligent culture we may obtain the perfect fruits. This therefore has reference to the world and the resurrection, the next to the soul and the body, as it follows, Nor of abramble bush gather they grapes. Either because no one living in sin obtains fruit to his soul, which like the grape nearest the ground is rotten, on the higher branches becomes ripe. Or because no one can escape the condemnations of the flesh, but he whom Christ has redeemed, Who as a grape hung on the tree.
“The good man produces good from the good treasure in his heart, and the evil man produces evil from the evil treasure.” The treasure in one’s heart is the intention of the thought, from which the Searcher of hearts judges the outcome….Christ subsequently adds force to his pronouncement by clearly showing that good speech without the additional attestation of deeds is of no advantage at all. He asks, “And why do you call me, ‘Lord, Lord,’ and not do what I say?” To call upon the Lord seems to be the gift of a good treasure, the fruit of a good tree. “For everyone who calls upon the name of the Lord will be saved.” If anyone who calls upon the name of the Lord resists the Lord’s commands by living perversely, it is evident that the good that the tongue has spoken has not been brought out of the good treasure in his heart. It was not the root of a fig tree but that of a thorn bush that produced the fruit of such a confession—a conscience, that is, bristling with vices, and not one filled...
“Every tree which does not bear fruit will be cut down and cast into the fire.” He is referring to human beings as trees and to their works as the fruit. Do you want to know which are the bad trees and what are the bad fruits? The apostle teaches us this. He says, “The works of the flesh are manifest: they are fornication, impurity, selfindulgence, idolatry, sorcery, malice, strife, jealousy, anger, quarrels, conflict, factions, envy, murder, drunkenness, carousing, and things of this sort.” Do you want to hear whether trees which bring forth fruits such as these belong in the heavenly temple of the eternal King? The apostle continues: “I warn you, as I warned you before, that those who do such things will not attain the kingdom of God.” He subsequently lists the fruits of a good tree. He says, “The fruit, however, of the Spirit is charity, joy, peace, patience, goodness, kindness, faith, gentleness, selfcontrol.”
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 figis 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 enclosed and supported by ahedge, 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.
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.
See again, Christ commands that those who come to us must be distinguished not by their clothing but by what they really are. “By its fruit,” he says, “the tree is known.” It is ignorance and folly for us to expect to find the choicer kinds of fruits on thorns, grapes for instance, and figs. So it is ridiculous for us to imagine that we can find in hypocrites and the profane anything that is admirable, such as the nobleness of virtue….This is also made clear by another declaration of our Lord. “The good man,” he says, “as out of a good treasure, pours forth from the heart, good things.” One who is differently disposed, and whose mind is the prey of fraud and wickedness, necessarily brings forth what is concealed deep within. The things that are in the mind and heart boil over and are vomited forth by the stream of speech that flows out of it. The virtuous person therefore speaks such things as become his character, while one who is worthless and wicked vomits forth his secret impurity....
Each man's life also will be a criterion of his character. For not by extrinsic ornaments and pretended humility is the beauty of true happiness discovered, but by those things which a man does; of which he gives an illustration, adding, For of thorns men do not gather figs.
But having shown that the good and the bad man may be discerned by their works as a tree by its fruits, he now sets forth the same thing by another figure, saying, A good man out of the good treasure of his heart brings forth that which is good, and the evil man out of the evil treasure brings forth that which is evil.
He does not then exclude repentance, but a continuance in evil, which aslong as it is evil cannot bring forth good fruit, but being converted to virtue, will yield abundance. But what nature is to the tree, our affections are to us. If then a corrupt tree cannot bring forth good fruit, how shall a corrupt heart?
But although the fruit is caused by the tree, yet, it brings to us the knowledge of thetree, because the distinctive nature of the tree is made evident by the fruit, as it follows, Forevery tree is know by its fruit.
For it is a natural consequence when wickedness abounds within, that wicked words are breathed as far as the mouth; and therefore when you hear of a man uttering abominable things, do not suppose that there lies only so much wickedness in him as is expressed in his words, but believe the fountain to be more copious than the stream.
In order that they may be able to establish and settle their threefold theory, or "trinity "in all its characteristics as to the several natures, because "a good tree cannot produce evil fruit, nor a corrupt tree good fruit; and nobody gathers figs of thorns, nor grapes of brambles.".
Of his conceit from the simple passage of our Lord's saying, which has reference to human beings and not divine ones, wherein He disposes of those examples of a good tree and a corrupt one;
But take not these words to thyself as an encouragement to idleness, for the tree is moved conformably to its nature but you have the exercise of free will; and every barren tree has been ordained for some good, but you were created to the good work of virtue.