At that time: Jesus spoke this parable unto the multitudes: The Kingdom of heaven is likened unto a man which sowed good seed in his field.
Sermon of St Augustine
In this parable the Lord hath reference to the time when the Shepherds of the Church should begin to wax careless, (or, it may be, to the time when the Apostles should fall asleep in the sleep of death,) at which time, the devil would come and sow that which the Lord calleth a seed of evil-doers. Now, is this seed of evil-doers a reference to heretics or to Catholics of bad lives? It certainly is not unjust to call the heretics a seed of evil-doers, seeing that they have sprung up from the seed of the Gospel, and have been begotten in the Name of Christ, and afterwards have turned into crooked ways and lying doctrines.
But since it is written that this seed was sown in the midst of the wheat, we ought perhaps to understand thereby a reference to such as are of one Communion with the righteous. However, inasmuch as the Lord saith: The field is the world: and doth not thereby directly speak of the Church, we may with good reason understand the seed of evil-doers to be the heretics, since in this world they are mingled together with the good, not in one common Communion, but only under one common name of Christian. And Catholics of bad lives, which nevertheless are of one Faith with the good seed, and yet are themselves worthless, may more fitly be likened to straw than to tares, since the straw springeth from one soil and one root with the good grain-bearing ear of corn.
However, as touching the net cast into the sea, and enclosing a great multitude of fishes, both bad and good, we may well understand that by the bad are meant Catholics of bad lives. For the sea is one thing whereby we may understand to be signified the world; and the net another, which seemeth to signify our Faith, or the Communion of one Church. Between heretics and sinful Catholics there is this difference: heretics believe a lie: sinful Catholics believe the truth, but live not what they believe.