So the people of Nineveh believed God, and proclaimed a fast, and put on sackcloth, from the greatest of them even to the least of them.
Read Chapter 3
Ambrose of Milan
If the apostle said too little [about fasting], let them hear the prophet [in the psalm] saying, “I afflicted my soul with fasting.” One who does not fast is uncovered and naked and exposed to wounds. Finally, if Adam had uncovered himself with fasting, he would not have become naked. Nineveh freed itself from death by fasting. The Lord himself said, “But this kind of demon will be cast out only by prayer and fasting.”
God. They were convinced that he had wrought such wonders in the person of Jonas, with a desire of their welfare, particularly as he allowed them some delay. Accordingly they did penance for about forty days, and their conversion was so sincere, that Christ proposes it to his disciples, Matthew xii. 41. (Calmet)
Thus "the city was overturned in its perverse manners. "(St. Augustine, City of God xxi. 24., and Psalm l.)
They were at an end, and the city was renovated. (Haydock)
Let us sow in tears, so that we may reap in joy. Let us show ourselves people of Nineveh, not of Sodom. Let us amend our wickedness, lest we be consumed with it. Let us listen to the preaching of Jonah, lest we be overwhelmed by fire and brimstone. And if we have departed from Sodom, let us escape to the mountain. Let us flee to Zoar. Let us enter it as the sun rises. Let us not stay in all the plain. Let us not look around us, lest we be frozen into a pillar of salt, a really immoral pillar, to accuse the soul that returns to wickedness. On His Father’s Silence, Oration
LXX: similar. Nineveh believed but Israel did not believe; the foreskin believed, but circumcision remained without faith. First of all the men of Nineveh believed who had arrived at the age of Christ: they announced a fast and dressed in sackcloth, from the greatest to the smallest of them. This regime and clothing is very worthy of penitence, so that those who had offended God through their indulgence or lust appeased him by condemning all that they had previously offended with. Sackcloth and fasting are the weapons of penitence, the rescue of sinners. First of all fasting, then sackcloth; first of all what is not seen, then what is visible; the one is always shown to God, the other sometimes to man. And if it were necessary to remove one from the two then I would rather keep fasting without sackcloth than have sackcloth without fasting. Elder men give the example which pertains to youths: for no one is without sin; and if his life only lasted one day, the years of his life woul...
Do you see how vexed God is when fasting is treated despitefully? Learn how delighted he is when fasting is honored. When Eve was maltreated, he inflicted death as a penalty upon the insolent individual. He revoked death when she was honored once again. Desiring to show you the power of this thing of importance, he gave her authority over the sentence, after the arrest, to snatch the prisoners from the middle of the journey and change their course toward life. And he did this not only for two or three or twenty people but also for a whole population, in the case of the great and marvelous city of the Ninevites, which had knelt and bowed its head over this pit of perdition and was expecting to suffer the blow from above. Like a heavenly power overseeing Nineveh’s charge, fasting snatched the city from these gates of death and returned Nineveh to life.