Question: "When did Moab and Ammon eventually worship the Lord (Zephaniah 2:11)?"
Answer: Zephaniah 2:11 proclaims that the people of Moab and Ammon would eventually worship the Lord. Immediately after predicting the destruction of Moab and Ammon, the prophet says, “The LORD will be awesome to them when he destroys all the gods of the land. The nations on every shore will worship him, every one in its own land.” Has this already taken place? If so, when did it happen? If not, when will it take place?
The larger context of this section of Zephaniah details God’s judgment on the non-Jewish nations. The judgment spread in all four directions around Judah—the Philistines (to the west, 2:4-7), Moab and Ammon (to the east, 2:8-11), Ethiopia (to the south, 2:12), and Assyria (to the north, 2:13-15). Along with the judgments is a promise that people from all the nations would one day worship the Lord (cf. Malachi 1:11). We have not yet seen these nations worship the Lord. That aspect of Zephaniah’s prophecy has not yet been fulfilled and must therefore take place in the future.
The prophet predicts that Moab and Ammon will be destroyed “like Sodom and Gomorrah” (Zephaniah 2:9). Such total annihilation calls to mind the devastation that will take place in the tribulation period, referenced in the books of Daniel and Revelation. Judgment will come upon the earth, concluding with a battle at Armageddon (Revelation 19:11-21). At that point, the Messiah (Jesus) will return and reign from His throne in Jerusalem for a 1,000-year time period known as the millennium (Revelation 20:1-6).
The prophet Zechariah says that, during this millennial kingdom, the nations of the world will worship the Lord Jesus: “Then the survivors from all the nations that have attacked Jerusalem will go up year after year to worship the King, the LORD Almighty, and to celebrate the Feast of Tabernacles” (Zechariah 14:16). This would include remnants of the ancient nations of Moab and Ammon.
The many references in Zephaniah to the “Day of the Lord” indicate a time yet to come when peace and justice will rule because Jesus Himself has taken up His rightful throne.