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.”
Related Commentaries of Joel 3:9
Joel 3:9
9 Proclaim ye this among the Gentiles; Prepareb war, wake up the mighty men, let all the men of war draw near; let them come up: