Jeremiah 6:8

Behold the mercy and piety of the good God. When he wishes to be merciful, he says that he is displeased and angry. As he says through Jeremiah, "You will be chastised, Jerusalem, with pain and a scourge, lest my soul depart from you." If you understand these words, it is the voice of God having compassion when he is angry, when he is jealous, when he brings pains and beatings. "For he scourges every one whom he receives."

(Verse 8) Iniquity and devastation will be heard in it before me always, weakness and affliction. Learn, Jerusalem, lest my soul may depart from you, lest I make you deserted, an uninhabitable land. LXX: Impiety and misery will be heard in it before its face. Through every pain and scourge you will be taught, Jerusalem, lest my soul may depart from you: lest I make you an impassable land, a land that is not inhabited. Through these things we learn that the Lord chastises every son whom he receives. And for this reason Jerusalem is chastised with blows and torments, so that it may be corrected, and the soul of God does not depart from it, and it is brought into solitude. Therefore, if at any time we are subjected to frequent trials, let us remember for our consolation this verse: Through all pain and scourge you shall be taught, O Jerusalem.

It was that thou mayest learn that God silently and noiselessly observes the affairs of men, and watches the course of each one's life; and so it is written, "The paths of a man are before the eyes of God; and He looks at all his tracks." And as He is good, and willeth that all men should be saved, He often purifies those who are entangled in sins by inflicting sickness upon their body. For so He somewhere says by the voice of Jeremiah, "Thou shalt be taught, O Jerusalem, by labour and the scourge." And the writer of the book of Proverbs also has somewhere said, "My son, despise not thou the teaching of the Lord, nor faint when thou art convicted by Him, for whom the Lord loveth, He chasteneth, and scourgeth every son whom He accepteth." Well, therefore, does Christ announce that He will cut away the cause of the disease, and the very root, as it were, of the malady, even sin: for if this be removed, necessarily must the disease which sprung from it be also at the same time taken away.