Joel 3 looks ahead to when God restores His people. In those days, and in that time, when I restore the fortunes of Judah and Jerusalem, God says, I will gather all nations, and will bring them down into the valley of Jehoshaphat; and I will execute judgment on them there for my people. The name Jehoshaphat means Yahweh judges. The nations had scattered God's people and carried off His treasures.
God turns a famous peace saying around. Instead of beating swords into plowshares, the nations are told, Beat your plowshares into swords, and your pruning hooks into spears. Let the weak say, I am strong. It is a call to gather for judgment. Multitudes, multitudes in the valley of decision! The harvest is ripe, for their wickedness is great. Christians believe this points to God's final judgment, without knowing its day.
Joel ends with security and blessing for God's people. Yahweh will roar from Zion, and thunder from Jerusalem; and the heavens and the earth will shake; but Yahweh will be a refuge to his people, and a stronghold to the children of Israel. Then: the mountains will drop down sweet wine, the hills will flow with milk. A fountain will flow out from Yahweh's house. But Judah will be inhabited forever, and Jerusalem from generation to generation. The last words are, for Yahweh dwells in Zion.