Zachariah 8:18 The word of the Lord Almighty came to me. This is what the Lord Almighty says: “The fasts of the fourth, fifth, seventh and tenth months will become joyful and glad occasions and happy festivals for Judah. Therefore love truth and peace.”
2 Kings 25:3-4 On the ninth day of the fourth month the famine was so severe in the city that there was no food for the people of the land. Then a breach was made in the city, and all the men of war fled by night
Jeremiah 52:12-15 In the fifth month, on the tenth day of the month—that was the nineteenth year of King Nebuchadnezzar, king of Babylon—Nebuzaradan the captain of the bodyguard, who served the king of Babylon, entered Jerusalem. And he burned the house of the LORD, and the king’s house and all the houses of Jerusalem; every great house he burned down. And all the army of the Chaldeans, who were with the captain of the guard, broke down all the walls around Jerusalem.
Jeremiah 41:1-3 In the seventh month, Ishmael the son of Nethaniah, son of Elishama, of the royal family, one of the chief officers of the king, came with ten men to Gedaliah the son of Ahikam, at Mizpah. As they ate bread together there at Mizpah, Ishmael the son of Nethaniah and the ten men with him rose up and struck down Gedaliah the son of Ahikam, son of Shaphan, with the sword, and killed him, whom the king of Babylon had appointed governor in the land.
Jeremiah 52:4 And in the ninth year of his reign, in the tenth month, on the tenth day of the month, Nebuchadnezzar king of Babylon came with all his army against Jerusalem, and laid siege to it. And they built siegeworks all around it.
The fasts recorded in vs. 19 were instituted by man in the remembrance of their sin and the curse of God that fell upon them. They wanted to remember how they did not honor, glorify, or obey God, and because of this they angered God and were punished. They did not want to repeat this again. Here we read of God promising blessing.
Campbell Morgan said of these man-appointed fasts: “None of these things had been in the purpose of God for His people; they had resulted from their sins. The fasts, therefore, were the result of their sins. In jealousy and fury, the outcome of love, Jehovah would put away their sins, and so restore them to true prosperity. On that day, let them still remember and observe, only let the observance be a feast in celebration of God’s grace, instead of a fast in memory of their sin.” We can get hung up on our past sins and forget the blessings of forgiveness. Peter put it this way; 2Peter 1:3 His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence, by which he has granted to us his precious and very great promises, so that through them you may become partakers of the divine nature, having escaped from the corruption that is in the world because of sinful desire. For this very reason, make every effort to supplement your faith with virtue, and virtue with knowledge, and knowledge with self-control, and self-control with steadfastness, and steadfastness with godliness, and godliness with brotherly affection, and brotherly affection with love. For if these qualities are yours and are increasing, they keep you from being ineffective or unfruitful in the knowledge of our Lord Jesus Christ. For whoever lacks these qualities is so nearsighted that he is blind, having forgotten that he was cleansed from his former sins. Therefore, brothers, be all the more diligent to confirm your calling and election, for if you practice these qualities you will never fall.