22 Here they say; “It is true both kinds did once grow throughout the world, but the good wheat is diminished, and confined to this our country, and our small communion.” But the Lord does not allow you to interpret as you will. He who explains this parable Himself, shuts your mouth, your sacrilegious, profane, and ungodly mouth, that is counter to your own interests, while you run counter to the testator, even as he calls you to the inheritance. How does He shut your mouth?
By saying, “Let both grow together until the harvest.” If the harvest has come already, let us believe that the wheat has been diminished. Though not even then shall it be diminished, but gathered up into the barn. For so He says, “Gather ye together first the tares, and bind them in bundles to burn them, but gather the wheat into My barn.” If then they grow until the harvest, and after the harvest are gathered in, how are they diminished, you wicked, you ungodly one? I grant that in comparison with the tares and chaff the wheat is less in quantity; still “both grow together until the harvest.”
For “when iniquity abounds, the love of many waxes cold;” the tares and the chaff multiply. But because throughout the whole world wheat cannot be wanting, which “by enduring unto the end shall be saved, both grow together until the harvest.” And if because of the abundance of the wicked it is said, “When the Son of Man comes, do you think, shall He find faith on the earth?” and by this denomination are signified all those who by transgression of the law imitate him to whom it was said, Earth you are, and unto earth shall you return; yet because of the abundance of the good also, and because of him to whom it was said, “Your seed shall be as the stars of heaven, and as the sand of the sea;” is that also written, “Many shall come from the East and West, and shall sit down with Abraham, and Isaac, in the kingdom of God.” “Both” then “grow together until the harvest,” and both the tares or chaff have their passages in the Scriptures, and the wheat theirs.
And they who do not understand them, confound them and are themselves confounded; and in their blind desire they make such an uproar, that they will not be silenced even by the clear manifestation of the truth.
Source: Sermons on Selected Lessons of the New Testament (New Advent)