The Bible Says Commentary on the Book of Joel
Joel 3 deals with the judgment of the nations, including the four nations who invaded Israel, and the restoration of Judah. The LORD will assemble all the Gentile nations in the valley of Jehoshaphat (the valley of decision). There He will judge them for their unbelief and their mistreatment of His covenant people. In those days, Judah will enjoy the fullness of God’s blessings and will live peaceably. The land of Judah will prosper once again because the LORD will dwell in it forever.