John Gill 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)

And he said, hearken you, all Judah, and you inhabitants of Jerusalem, and thou King Jehoshaphat There is a climax or gradation in these words rising from the lowest to the highest; from the people of the cities in the country, to the inhabitants of Jerusalem the metropolis, and from thence to the king the supreme governor: thus saith the Lord unto you, be not afraid, nor dismayed, by reason of this great multitude ; whose numbers were discouraging to the king, and he had taken notice of them, which this respects: for the battle is not your's, but God's : the cause was his, and he would espouse and maintain it; not they, but he, would fight the battle, and therefore they had nothing to fear.