Commenting on Matthew 15:19 (PG 77, 184-185):
Whence is it that evil thoughts come forth from the heart, and defile a man? Doubtless, because the labourers are asleep who should be keeping watch, so as to safeguard and preserve the fruits of good seed that is growing up. For unless we have weakened in our vigilance, by gluttony and by sloth, defiling the divine image, that is, corrupting the good seed, the sower of tares [the devil] would not have found a way to creep up on us, nor would he have sown within us tares worthy of the fire; that is, “evil thoughts which come forth from the heart and which defile a man”.
“Wilt thou that we go and gather it up?” Thus speak the Angels, ever prepared with eager devotion to serve the divine will, as they see our inactivity and sloth, and the infinite forbearance of God. But they are forbidden, lest they uproot the good wheat together with the tares, that is, so that the sinner may not be cut off while in his mind there is yet a possibility of repentance; lest innocent children be destroyed together with their parents, who though perhaps yet in their parents’ loins, nevertheless with God, who sees all things, they already are.
For the ranks of the Angels, fellow servants of creation, know not the things that as yet exist not. But God both knows and has wrought because of these very circumstances. For He did not cut off the evil-doing Esau, who had not yet begotten; lest together with him Job might also perish, who from him took descent. Nor did he slay Matthew, who had given himself to the exacting of the tribute, so that He might not thus impede the preaching of the gospel. Neither did He destroy the harlots who served lust and immodesty, lest models of repentance might be wanting. He avenged not Peter’s denial, because already He beheld his burning tears of repentance. Nor did he strike down with death the persecuting Saul, lest the ends of the earth be deprived of salvation.
All tares therefore that await the time of the harvest, and do not change themselves into fruits of repentance, are being made ready for the great fire, since they have flowered wholly into fruitlessness. But they whose roots are deep, whose ears of corn are abundant, who are bending over at harvest time with the weight of fruit and all but calling for the sickle of the harvesters, these Christ orders to be carried by the Angels to the heavenly seats, to share their joy, to reign with Him, and be sharers of His immortal happiness, who with the Father and the Holy Spirit liveth and reigneth world without end. Amen.
Excerpt taken from the book: The Sunday Sermons of the Great Fathers, Vol 1.