The possibility of repentance is a reason why baptism should not be deferred to old age, a practice which is against the will of God in holy Scripture. But it is of no use to practise penance whilst still serving lusts. These must be first subdued.
98. Good, then, is penitence, and if there were no place for it, every one would defer the grace of cleansing by baptism to old age. And a sufficient reason is that it is better, to have a robe to mend, than none to put on; but as that which has been repaired once is restored, so that which is frequently mended is destroyed.
99. And the Lord has given a sufficient warning to those who put off repentance, when He says: “Repent, for the kingdom of heaven is at hand.” We know not at what hour the thief will come, we know not whether our soul may be required of us this next night. God cast Adam out of Paradise immediately after his fault; there was no delay. At once the fallen were severed from all their enjoyments that they might do penance; at once God clothed them with garments of skins, not of silk.
100. And what reason is there for putting off? Is it that you may sin yet more? Then because God is good you are evil, and “despise the riches of His goodness and long-suffering.” But the goodness of the Lord ought rather to draw you to repentance. Wherefore holy David says to all: “Come, let us worship and fall down before Him, and mourn before our Lord Who made us.” But for a sinner who has died without repentance, because nothing remains but to mourn grievously and to weep, you find him groaning and saying: “O my son Absalom! My son Absalom!” For him who is wholly dead mourning is without alleviation.
101. But of those who as exiles and banished from their ancestral homes, which the holy law of Moses had assigned them, will be entangled in the errors of the world, you hear him saying: “By the waters of Babylon we sat down and wept, when we remembered Zion.” He sets forth the wailings of those who have fallen, and shows that they who are living in this condition of passing time and changing circumstances ought to repent, after the example of those who, as a reward for sin, had been led into miserable captivity.
102. But nothing causes such exceeding grief as when any one, lying under the captivity of sin, calls to mind whence he has fallen, because he turned aside to carnal and earthly things, instead of directing his mind in the beautiful ways of the knowledge of God.
103. So you find Adam concealing himself, when he knew that God was present, and wishing to be hidden when called by God with that voice which wounded the soul of him who was hiding: “Adam, where are you?” That is to say, Wherefore hidest you yourself? Why are you concealed? Why do you avoid Him, Whom you once longed to see? A guilty conscience is so burdensome that it punishes itself without a judge, and wishes for covering, and yet is bare before God.
104. And so no one in a state of sin ought to claim a right to or the use of the sacraments, for it is written: “You have sinned, be still.” As David says in the Psalm lately quoted: “We hanged our harps upon the willows in the midst thereof;” and again: “How shall we sing the Lord's song in a strange land?” For if the flesh wars against the mind, and is not subject to the guidance of the Spirit, that is a strange land which is not subdued by the toil of the cultivator, and so cannot produce the fruits of charity, patience, and peace. It is better, then, to be still when you cannot practise the works of repentance, lest in the very acts of repentance there be that which afterward will need further repentance. For if it be once entered upon and not rightly carried out, it obtains not the result of a first repentance and takes away the use of a later one.
105. When, then, the flesh resists, the soul must be intent upon God, and if results do not follow, let not faith fail. And if the enticements of the flesh come upon us, or the powers of the enemy attack us, let the soul keep in submission to God. For we are then specially oppressed when the flesh yields. And some there are who trouble heavily the wretched soul, seeking to deprive it of all protection. To which case the words apply: “Rase it, rase it, even to the foundations.”
106. And David, pitying her, says: “O wretched daughter of Babylon.” Wretched indeed, as being the daughter of Babylon, when she ceased to be the daughter of Jerusalem. And yet he calls for a healer for her, and says: “Blessed is he who shall take your little ones and dash them against the rock.” That is to say, shall dash all corrupt and filthy thoughts against Christ, Who by His fear and His rebuke will break down all motions against reason, so as, if any one is seized by an adulterous love, to extinguish the fire, that he may by his zeal put away the love of a harlot, and deny himself that he may gain Christ.
107. We have then learned that we must do penance, and this at a time when the heat of luxury and sin is giving way; and that we, when under the dominion of sin, must show ourselves Godfearing by refraining, rather than allowing ourselves in evil practices. For if it is said to Moses when he was desiring to draw nearer: “Put off your shoes from off your feet,” how much more must we free the feet of our soul from the bonds of the body, and clear our steps from all connection with this world.
Source: On Repentance (New Advent)