Whenever Israel was threatened from the north, it was tempted to turn to Egypt for aid (cf. chs. 30-31). Isaiah was vehemently opposed to this: “Trust God alone and do not rely on human forces” was his persistent message.
Isaiah sees Yahweh coming against Egypt in judgment. The action will result in complete chaos within Egyptian society, which was world renowned for its social stability. The effect will be (1) civil war (v. 2), (2) a sense of desperation (v. 3), and (3) a tyrannical government (v. 4). The death of Egyptian society is symbolized in the death of the heart of Egypt, the Nile (vv. 5-10). Without the Nile, there would be no Egypt. Farmers, fishermen, weavers, and merchants were all dependent on the mighty river. There is a total breakdown of society (vv. 11-15). The cornerstones (v. 13), or leaders, have led the people astray. In the end, Egypt will be completely impotent (v. 15).
A marked change occurs in both style (from poetry to prose) and tone (from judgment to redemption) in the latter half of ch. 19. Isaiah reinforces his point that Judah should not turn to Egypt. Reason number 1: Egypt will be nearly devastated by God's judgment. Reason number 2: Eventually Egypt itself will turn to God.
“Five cities” (v. 18) probably refers to a few or a small number, enough for a sign and witness to God (v. 20). The NIV notes that the Dead Sea Scroll reads “city of the Sun” rather than City of Destruction. In Hebrew, the two terms would be easily confused, and the former is correct.
Vv. 20b-22 are allusions to the Exodus, with a significant twist, “When they [the Egyptians] cry out to the Lord because of their oppressors [as the Hebrew slaves had done], he will send them a savior and defender [as he sent Moses], and he will rescue them.” The Egyptians will acknowledge Yahweh as God. The plagues with which God struck them will now be used to heal them. Eventually the great empires of the earth, Egypt and Assyria, along with Israel, will one day worship the Lord.