Here God does not make his prophet wait any longer. He links up to the challenging language of his prophet. God thereby indicates: if my people repent (Joel 2:18) I am actually going to save them (as he promised to do). The people do not have to fight for this; they may gratefully receive the victory (see 2 Chronicles 20:1–37).
12 Let the nations stir themselves up and come up to the Valley of Jehoshaphat; for there I will sit to judge all the surrounding nations.