Charles Ellicott Commentary 2 Chronicles 20:15

"and he said, Hearken ye, all Judah, and ye inhabitants of Jerusalem, and thou king Jehoshaphat: Thus saith Jehovah unto you, Fear not ye, neither be dismayed by reason of this great multitude; for the battle is not yours, but God`s." — 2 Chronicles 20:15 (ASV)

Listen. —So Isaiah 49:1; Isaiah 51:4, and so on.

Be not afraid nor dismayed. —Isaiah 51:7; Deuteronomy 1:21; 1 Chronicles 22:3; 2 Chronicles 20:17, referenced below.

Great multitude —that is, “great company” (2 Chronicles 20:12).

The battle is not yours, but God's. —Compare David's words to Goliath, “The battle is Jehovah’s” (1 Samuel 17:47); and the Divine title Jehovah Sabaoth, that is, Jehovah, the leader of the hosts of Israel. “It was on the battle-field that Jehovah’s presence was most clearly realised.”—Prof. Robertson Smith. (Psalms 46:7; Psalms 46:9.)