Jamieson, Fausset and Brown on 2 Chronicles 23:4-9

4-9. This is the thing that ye shall do--The arrangements made for defense are here described. The people were divided into three bodies; one attended as guards to the king, while the other two were posted at all the doors and gates, and the captains and military officers who entered the temple unarmed to lull suspicion, were furnished with weapons out of the sacred armory, where David had deposited his trophies of victory and which was reopened on this occasion.