Charles Ellicott Commentary 2 Chronicles 20:21

"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." — 2 Chronicles 20:21 (ASV)

And when he had consulted with. —Or, advised, given counsel to, warned. (Compare 2 Kings 6:8.) Vulgate, “deditque consilium populo, et statuit cantores domini.”

And that should praise the beauty of holiness. —Rather, and men praising, in holy apparel; that is, Levitical vestments (1 Chronicles 16:29; Psalms 29:2).

And to say. — And saying.

Praise the Lord. — Give thanks to Jehovah. The refrain of the singers. (See on 1 Chronicles 16:34; 1 Chronicles 16:41; 2 Chronicles 5:13; 2 Chronicles 7:3.) The band of Levitical minstrels was to march before the army (halûq, the armed host; Joshua 6:7).