15 Take heed lest without reason you mistrust the power of repentance. Would you know what power repentance has? Would you know the strong weapon of salvation, and learn what the force of confession is? Hezekiah by means of confession routed a hundred and fourscore and five thousand of his enemies. A great thing verily was this, but still small in comparison with what remains to be told: the same king by repentance obtained the recall of a divine sentence which had already gone forth.
For when he had fallen sick, Esaias said to him, Set your house in order; for you shall die, and not live. What expectation remained, what hope of recovery, when the Prophet said, for you shall die? Yet Hezekiah did not desist from repentance; but remembering what is written, When you shall turn and lament, then shall you be saved, he turned to the wall, and from his bed lifting his mind to heaven (for thickness of walls is no hindrance to prayers sent up with devotion), he said, “Remember me, O Lord, for it is sufficient for my healing that You remember me.
You are not subject to times, but art Yourself the giver of the law of life. For our life depends not on a nativity, nor on a conjunction of stars, as some idly talk; but both of life and its duration. Then art Yourself the Lawgiver according to Your Will.” And he, who could not hope to live because of the prophetic sentence, had fifteen years added to his life, and for the sign the sun ran backward in his course. Well then, for Ezekias' sake the sun turned back but for Christ the sun was eclipsed, not retracing his steps, but suffering eclipse, and therefore showing the difference between them, I mean between Ezekias and Jesus.
The former prevailed to the cancelling of God's decree, and cannot Jesus grant remission of sins? Turn and bewail yourself, shut your door, and pray to be forgiven, pray that He may remove from you the burning flames. For confession has power to quench even fire, power to tame even lions.
Source: Catechetical Lectures (New Advent)