21 And when he had taken counsel with the people, he appointed them that should sing unto Jehovah, and give praise in holy array, as they went out before the army, and say, Give thanks unto Jehovah; for his lovingkindness [endureth] for ever. 22 And when they began to sing and to praise, Jehovah set liers-in-wait against the children of Ammon, Moab, and mount Seir, that were come against Judah; and they were smitten. 23 For the children of Ammon and Moab stood up against the inhabitants of mount Seir, utterly to slay and destroy them: and when they had made an end of the inhabitants of Seir, every one helped to destroy another. 24 And when Judah came to the watch-tower of the wilderness, they looked upon the multitude; and, behold, they were dead bodies fallen to the earth, and there were none that escaped.

Matthew Henry's Commentary on 2 Chronicles 20:21-24

Commentary on 2 Chronicles 20:20-30

(Read 2 Chronicles 20:20-30)

Jehoshaphat exhorted his troops to firm faith in God. Faith inspires a man with true courage; nor will any thing help more to the establishing of the heart in shaking times, than a firm belief of the power, and mercy, and promise of God. In all our trust in the Lord, and our praises of him, let us especially look at his everlasting mercy to sinners through Jesus Christ. Never was an army so destroyed as that of the enemy. Thus God often makes wicked people destroy one another. And never was a victory celebrated with more solemn thanksgivings.