Joseph Benson's Commentary of the Old and New Testaments - 2 Chronicles 20:3
2 Chronicles 20:3. Jehoshaphat feared Partly from human frailty, and partly from the remembrance of his own guilt, and the wrath of God denounced against him for it, 2 Chronicles 19:2. And set himself to seek the Lord The phrase denotes his settled resolution, seriousness, and earnestness in it, and the preparing and fixing of his heart for it. And proclaimed a fast Partly in token of his humiliation and penitence for his sins, and partly to render himself and his people more fervent in... read more
Albert Barnes' Notes on the Whole Bible - 2 Chronicles 20:3
General fasts had been previously observed by the Israelites (e. g. Judges 20:26; 1 Samuel 7:6); but we do not hear of any fast having been “proclaimed” by authority before this. read more