Augustine of Hippo

(Quæst. in Matt. q. 11.) He says, While men slept, for while the heads of the Church were abiding in supineness, and after the Apostles had received the sleep of death, then came the Devil and sowed upon the rest those whom the Lord in His interpretation calls evil children. But we do well to enquire whether by such are meant heretics, or Catholics who lead evil lives. That He says, that they were sown among the wheat, seems to point out that they were all of one communion. But forasmuch as He interprets the field to mean not the Church, but the world, we may well understand it of the heretics, who in this world are mingled with the good; for they who live amiss in the same faith may better be taken of the chaff than of the tares, for the chaff has a stem and a root in common with the grain. While schismatics again may more fitly be likened to ears that have rotted, or to straws that are broken, crushed down, and cast forth of the field. Indeed it is not necessary that every heretic or schismatic should be corporally severed from the Church; for the Church bears many who do not so publicly defend their false opinions as to attract the attention of the multitude, which when they do, then are they expelled. When then the Devil had sown upon the true Church divers evil errors and false opinions; that is to say, where Christ’s name had gone before, there he scattered errors, himself was the rather hidden and unknown; for He says, And went his way. Though indeed in this parable, as we learn from His own interpretation, the Lord may be understood to have signified under the name of tares all stumbling-blocks and such as work iniquity.