Charles Ellicott Commentary Joel 3:9

"Proclaim ye this among the nations; prepare war; stir up the mighty men; let all the men of war draw near, let them come up." — Joel 3:9 (ASV)

Prepare war—Literally, sanctify war. It was to be taken up deliberately, and after due religious rites, according to the customs of the nations. They are thus challenged, or rather summoned, to a trial of strength with Jehovah at a typical “Armageddon.”