When will the promise that Israel will be made one nation under one king and cleansed be fulfilled?
It will be fulfilled at the Second Coming, when Christ returns to Jerusalem and the kingdom comes down from heaven. At that time He will be King, Israel will be made one nation and cleansed, becoming head of the nations, while other nations serve in a lesser role than the covenant people.
Les explains that the promise is fulfilled when the kingdom comes down from heaven over which Christ is going to be the King. At that time Israel will be made one nation under one king, no longer divided, and cleansed from idols and transgressions, so they shall be His people and He will be their God. Israel will be the head of the nations, and all other nations will be there but in a lesser role than the covenant people. Les also points to Zechariah 14, the Second Coming, when Christ actually returns to Jerusalem and His feet shall stand upon the Mount of Olives. He says this is not something to spiritualize; it means what it says.