Albert Barnes Commentary Jonah 3:5

"And the people of Nineveh believed God; and they proclaimed a fast, and put on sackcloth, from the greatest of them even to the least of them." — Jonah 3:5 (ASV)

And the people of Nineveh believed God; – strictly, “believed in God.” To “believe in God” expresses more heart-belief than “to believe God” in itself necessarily conveys. To believe God is to believe that what God says is true; “to believe in” or “on God” expresses not belief only, but that belief resting in God, entrusting itself and all its concerns to Him. It combines hope and trust with faith, and love too, since, without love, there cannot be trust. They therefore believed the preaching of Jonah, and that He, in whose name Jonah spoke, had all power in heaven and earth. But they believed further in His unknown mercies; they cast themselves upon the goodness of the previously “unknown God.” Yet they believed in Him as the Supreme God, the object of awe, the God אלהים 'ĕlohı̂ym (Jonah 3:5; Jonah 3:8), האלהים ha'ĕlohı̂ym (Jonah 3:9), although they did not know Him as He is, the Self-Existent One.

Jonah does not say how they were thus persuaded.

God the Holy Spirit relates the wonders of God’s omnipotence as common everyday things. They are no marvels to Him Who performed them. He commanded and they were done. He spoke with power to the hearts that He had made, and they were turned to Him. Any human means are secondary, utterly powerless, except in His hands Who alone does all things through whomever He does them. Our Lord tells us that Jonah himself was a sign unto the Ninevites.

Whether, then, the mariners spread the history, or however the Ninevites knew the personal history of Jonah, he, in his own person and in what befell him, was a sign to them. They believed that God, Who avenged his disobedience, would avenge theirs. They believed perhaps, that God must have some great mercy in store for them, Who not only sent His prophet so far from His own land to them who had never acknowledged Him, never worshiped Him, but had done such mighty wonders to subdue His prophet’s resistance and to make him go to them.

And proclaimed a fast and put on sackcloth – It was not, therefore, a repentance in word only, but in deed. A fast was at that time entire abstinence from all food until evening; the haircloth was a harsh garment, irritating and afflictive to the body. Those who did so were (as we may still see from the Assyrian sculptures) men of pampered and luxurious habits, uniting sensuality and fierceness. Yet this they did at once, and as it seems, for the 40 days.

They proclaimed a fast. They did not wait for the supreme authority. Time was urgent, and they would lose none of it. In this imminent peril of God’s displeasure, they acted as people would in a conflagration. People do not wait for orders to put out a fire, if they can, or to prevent it from spreading. Whoever they were who proclaimed it, whether those in inferior authority, each in his neighborhood, or whether it spread from man to man, as the news spread, it was done at once.

It seems to have been done by acclamation, as it were, one common cry out of the one common terror. For it is said of them, as one succession of acts, the men of Nineveh believed in God, and proclaimed a fast, and put on sackcloth from their great to their little, every age, sex, and condition. “Worthy of admiration is that remarkable speed and diligence in deciding what to do, which, although in the same city with the king, perceived that they must provide for the common and imminent calamity, not waiting to laboriously ascertain the king’s pleasure.” In a city 60 miles in circumference, some time would inevitably be lost before the king could be approached; and we know, in some measure, the forms required in approaching Eastern monarchs of old.