Why does it specify Egypt?
Rashi: They do not need rain, for the Nile river rises and gives water to them.
What is the significance that they will not have rain? They do not need rain, for they rely on the Nile!
Rashi citing Targum Yonasan: The Nile will not give water to them.
Radak: Indeed, their punishment will be only the plague (refer to 14:18:3:2).
What do we learn from "Asher Yigof Hashem"?
Rashi: This will be the punishment of Egypt, or all Goyim [that will not ascend].
Radak: They will be plagued like all the nations that came against Yerushalayim - "Hamek Besaro" (12). Malbim - they already came against Yerushalayim and were plagued then. They will be plagued a second time!
The previous verse said that nations that do not ascend will not receive rain. Our verse says that they will be plagued!
Malbim: They will not receive rain. When Egypt will be plagued for not ascending, the plague will strike also them.
