In poetic form, the prophecy of Joel proceeds back and forth with both his words by Holy Spirit, and the words of Yahweh, the LORD. The surrounding nations are called to war, called rush to a battle in the "valley of verdict" that they cannot win. The list of surrounding nations to be judged is expanded to include Edom and Egypt for their shedding of innocent blood. They will be reduced a desert wasteland. The LORD will exact vengeance for the shedding of innocent blood, then settle to reign in Jerusalem, on Zion.
