2 Chronicles 20:3 - Joseph Benson’s Commentary on the Old and New Testaments

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 their prayers.