St. Ambrose teaches out of the prophet Isaiah what they must do who have fallen. Then referring to our Lord's proverbial expression respecting piping and dancing, he condemns dances. Next by the example of Jeremiah he sets forth the necessary accompaniments of repentance. And lastly, in order to show the efficacy of this medicine of penance, he enumerates the names of many who have used it for themselves or for others.
40. But if they be not converted, do you at least repent, who by many a slip have fallen from the lofty pinnacle of innocence and faith. We have a good Lord, Whose will it is to forgive all, Who called you by the prophet and said: “I, even I, am He that blots out your transgressions, and I will not remember, but you remember that we may plead together.” “I,” He says, “will not remember, but remember,” that is to say, “I do not recall those transgressions which I have forgiven you, which are covered, as it were, with oblivion, but remember them. I will not remember them because of My grace, remember them in order to correction; remember, you may know that the sin is forgiven, boast not as though innocent, that you aggravate not the sin, but you will be justified, confess your sin.” For a shamefaced confession of sins looses the bands of transgression.
41. You see what God requires of you, that you remember that grace which you have received, and boast not as though you had not received it. You see by how complete a promise of remission He draws you to confession. Take heed, lest by resisting the commandments of God you fall into the offense of the Jews, to whom the Lord Jesus said: “We piped to you and you danced not; we wailed and you wept not.”
42. The words are ordinary words, but the mystery is not ordinary. And so one must be on one's guard, lest, deceived by any common interpretation of this saying, one should suppose that the movements of wanton dances and the madness of the stage were commended; for these are full of evil in youthful age. But the dancing is commended which David practised before the ark of God. For everything is seemly which is done for religion, so that we need be ashamed of no service which tends to the worship and honouring of Christ.
43. Dancing, then, which is an accompaniment of pleasures and luxury, is not spoken of, but spiritually such as that wherewith one raises the eager body, and suffers not the limbs to lie slothfully on the ground, nor to grow stiff in their accustomed tracks. Paul danced spiritually, when for us he stretched forward, and forgetting the things which were behind, and aiming at those which were before, he pressed on to the prize of Christ. And you, too, when you come to baptism, are warned to raise the hands, and to cause your feet wherewith you ascend to things eternal to be swifter. This dancing accompanies faith, and is the companion of grace.
44. This, then, is the mystery. “We piped to you,” singing in truth the song of the New Testament, “and you danced not.” That is, did not raise your souls to the spiritual grace. “We wailed, and you wept not.” That is, you did not repent. And therefore was the Jewish people forsaken, because it did not repent, and rejected grace. Repentance came by John, grace by Christ. He, as the Lord, gives the one; the other is proclaimed, as it were, by the servant. The Church, then, keeps both that it may both attain to grace and not cast away repentance, for grace is the gift of One Who confers it; repentance is the remedy of the sinner.
45. Jeremiah knew that penitence was a great remedy, which he in his Lamentations took up for Jerusalem, and brings forward Jerusalem itself as repenting, when he says: “She wept sore in the night, and her tears are on her cheeks, nor is there one to comfort her of all who love her. The ways of Sion do mourn.” And he says further: “For these things I weep, my eyes have grown dim with weeping, because he who used to comfort me is gone far from me.” We notice that he thought this the bitterest addition to his woes, that he who used to comfort the mourner had gone far from him. How, then, can you take away the very comfort by refusing to repentance the hope of forgiveness?
46. But let those who repent learn how they ought to carry it out, with what zeal, with what affection, with what intention of mind, with what shaking of the inmost bowels, with what conversion of heart: “Behold,” he says, “O Lord, that I am in distress, my bowels are troubled by my weeping, my heart is turned within me.”
47. Here you recognize the intention of the soul, the faithfulness of the mind, the disposition of the body: “The elders of the daughters of Sion sat,” he says, “upon the ground, they put dust upon their heads, they girded themselves with haircloth, the princes hung their heads to the ground, the virgins of Jerusalem fainted with weeping, my eyes grew dim, my bowels were troubled, my glory was poured on the earth.”
48. So, too, did the people of Nineveh mourn, and escaped the destruction of their city. Such is the remedial power of repentance, that God seems because of it to change His intention. To escape is, then, in your own power; the Lord wills to be entreated, He wills that men should hope in Him, He wills that supplication should be made to Him. You are a man, and willest to be asked to forgive, and do you think that God will pardon you without asking Him?
49. The Lord Himself wept over Jerusalem, that, inasmuch as it would not weep itself, it might obtain forgiveness through the tears of the Lord. He wills that we should weep in order that we may escape, as you find it in the Gospel: “Daughters of Jerusalem, weep not for Me, but weep for yourselves.”
50. David wept, and obtained of the divine mercy the removal of the death of the people who were perishing, when of the three things proposed for his choice he selected that in which he might have the most experience of the divine mercy. Why do you blush to weep for your sins, when God commanded even the prophets to weep for the people?
51. And, lastly, Ezekiel was bidden to weep for Jerusalem, and he took the book, at the beginning of which was written: “Lamentation, and melody, and woe,” two things sad and one pleasant, for he shall be saved in the future who has wept most in this age. “For the heart of the wise is in the house of mourning, and the heart of fools in the house of feasting.” And the Lord Himself said: “Blessed are you that weep now, for you shall laugh.”
Source: On Repentance (New Advent)