2 Chronicles 20:3
3, 4. Jehoshaphat . . . proclaimed a fast throughout all Judah—Alarmed by the intelligence and conscious of his total inability to repel this host of invaders, Jehoshaphat felt his only refuge was at the horns of the altar. He resolved to employ the aid of his God, and, in conformity with this resolution, he summoned all his subjects to observe a solemn fast at the sanctuary. It was customary with the Hebrew kings to proclaim fasts in perilous circumstances, either in a city, a district, or throughout the entire kingdom, according to the greatness of the emergency. On this occasion, it was a universal fast, which extended to infants (2Ch 20:13; see also Joe 2:15, 16; Jon 3:7).
Ezra 8:21
21. Then I proclaimed a fast there—The dangers to travelling caravans from the Bedouin Arabs that prowl through the desert were in ancient times as great as they still are; and it seems that travellers usually sought the protection of a military escort. But Ezra had spoken so much to the king of the sufficiency of the divine care of His people that he would have blushed to apply for a guard of soldiers. Therefore he resolved that his followers should, by a solemn act of fasting and prayer, commit themselves to the Keeper of Israel. Their faith, considering the many and constant perils of a journey across the Bedouin regions, must have been great, and it was rewarded by the enjoyment of perfect safety during the whole way.
Joel 1:14
14. Sanctify . . . a fast—Appoint a solemn fast.
solemn assembly—literally, a "day of restraint" or cessation from work, so that all might give themselves to supplication (Joe 2:15, 16; 1Sa 7:5, 6; 2Ch 20:3-13). elders—The contrast to "children" (Joe 2:16) requires age to be intended, though probably elders in office are included. Being the people's leaders in guilt, they ought to be their leaders also in repentance. Joel 2:15
15. Blow the trumpet—to convene the people (Nu 10:3). Compare Joe 1:14. The nation was guilty, and therefore there must be a national humiliation. Compare Hezekiah's proceedings before Sennacherib's invasion (2Ch 30:1-27).
Jonah 3:5
5. believed God—gave credit to Jonah's message from God; thus recognizing Jehovah as the true God.
fast . . . sackcloth—In the East outward actions are often used as symbolical expressions of inward feelings. So fasting and clothing in sackcloth were customary in humiliation. Compare in Ahab's case, parallel to that of Nineveh, both receiving a respite on penitence (1Ki 21:27; 20:31, 32; Joe 1:13). from the greatest . . . to the least—The penitence was not partial, but pervading all classes.