All the survivors from the godless nations that fought against Jerusalem will travel to Jerusalem every year to worship the King, God-of-the-Angel-Armies, and celebrate the Feast of Booths.
If any of these survivors fail to make the annual pilgrimage to Jerusalem to worship the King, God-of-the-Angel-Armies, there will be no rain.
If the Egyptians don't make the pilgrimage and worship, there will be no rain for them. Every nation that does not go up to celebrate the Feast of Booths will be hit with the plague.
Egypt and any other nation that does not make pilgrimage to celebrate the Feast of Booths gets punished.