Joel 3:1-15 speaks concerning the judgment of Christ upon the nations—the judgment upon the living (Acts 10:42; 17:31).
This judgment will take place at the valley of Jehoshaphat, which is the valley of decision (Joel 3:2, 12, 14).
The purpose of Christ’s judgment upon the living will be to recompense the nations’ mistreatment of Israel during the great tribulation (vv. 2b-8; Rev. 12:17; 13:7, 10; Matt. 25:41-46a). After Christ casts Antichrist and the false prophet into the lake of fire, He will set up His throne in Jerusalem, and all the living ones as the goats and the sheep will be gathered before Him to be judged by Him. The goats will be the evil ones, those who persecuted the Jews, and the sheep will be the good ones, those who helped the persecuted Jews during the tribulation.
Finally, Joel speaks regarding the victory of Christ with His overcomers over the nations and His reign among Israel in the age of restoration (3:9-13, 16-21).
First, according to verses 9 through 13, Christ with His overcomers (Rev. 17:14; 19:11-14) as the mighty ones will defeat Antichrist and his armies (the nations) at Armageddon.
After the defeat of Antichrist, Christ will reign among Israel on the holy mountain of Zion within Jerusalem (Joel 3:16a, 17, 21b).
As Christ reigns in Jerusalem, He will be a shelter and a stronghold to the children of Israel (v. 16b). Because of this, no one will be able to damage Israel anymore.
Christ’s reign among Israel on the holy mountain of Zion within Jerusalem will be in the restoration (v. 18; Matt. 19:28).
Joel 3:18a tells us that in the restoration the mountains will drop down fresh wine, and the hills will flow with milk. This indicates how rich the situation will be.
In the restoration there will be no shortage of water, for all the waterways of Judah will flow with water (v. 18b). Wherever there is a waterway, there will be a river full of water.
A fountain will go forth from the house of Jehovah, the temple, to water the entire holy land (v. 18c). This points to the situation in the New Jerusalem, where a river will flow out of the throne of God and of the Lamb to water the holy city.
Joel 3:19-21a tells us that all the surrounding enemies of Israel will be punished. Therefore, the nations will be punished, Israel will be restored, and Christ will be manifested. This will be a prelude to the new heaven and new earth with the New Jerusalem.