Catena Aurea on Matthew 13:24–30: Augustine of Hippo

For when any one of the number of Christians included in the Church is found in such sin as to incur an anathema, this is done, where danger of schism is not apprehended, with tenderness, not for his rooting out, but for his correction. But if he be not conscious of his sin, nor correct it by penitence, he will of his own choice go forth of the Church and be separated from her communion; whence when the Lord commanded, “Suffer both to grow together till the harvest,” He added the reason, saying, “Lest when ye would gather out the tares ye root up the wheat also.” This sufficiently shews, that when that fear has ceased, and when the safety of the crop is certain, that is, when the crime is known to all, and is acknowledged as so execrable as to have no defenders, or not such as might cause any fear of a schism, then severity of discipline does not sleep, and its correction of error is so much the more efficacious as the observance of love had been more careful.

But when the same infection has spread to a large number at once, nothing remains but sorrow and groans. Therefore let a man gently reprove whatever is in his power; what is not in let him bear with patience, and mourn over with affection, until He from above shall correct and heal, and let him defer till harvest-time to root out the tares and winnow the chaff. But the multitude of the unrighteous is to be struck at with a general reproof, whenever there is opportunity of saying aught among the people; and above all when any scourge of the Lord from above gives opportunity, when they feel that they are scourged for their deserts; for then the calamity of the hearers opens their ears submissively to the words of their reprover, seeing the heart in affliction is ever more prone to the groans of confession than to the murmurs of resistance.

And even when no tribulation lays upon them, should occasion serve, a word of reproof is usefully spent upon the multitude; for when separated it is wont to be fierce, when in a body it is wont to mourn.