Ancient idol-worshippers believed that the fortunes of their countries were directly tied to the strength of their gods. Therefore, if another country was to conquer theirs, they would have no problem transferring their worship and loyalty to the invaders’ gods, as these were clearly stronger. Against that background, what Yeshayahu says to the people in this verse is quite revolutionary: Not only are the Assyrian gods non-existent, but Hashem Himself controls the Assyrians, and is using them as an instrument to punish Israel. Should the People of Israel return to God and practice justice and righteousness, however, Hashem will break the Assyrian yoke of oppression and punish the Assyrians for their arrogance. Yeshayahu’s eternal message to the Children of Israel is that God is always the cause of everything that occurs to them, and the nature of their fortune will be determined only on the basis of their record of adherence to His laws.