What does Isaiah 19:9 mean?

Ancient Egypt's wealth, strength, and power were all dependent on the Nile River. The Lord is showing Judah that Egypt (Isaiah 19:1–4) would become a husk of its former self. Under God's judgment, drying up the river (Isaiah 19:5–6), Egypt would lose one industry after another (Isaiah 19:7–8). The farmlands created by the annual flooding would cease to provide impressive crops of wheat. The fishing industry would be over. But the nation's dependence on the river went far beyond those industries.

Here Isaiah describes the despair of those who work in the linen industry. Egypt is still famous for its cotton, as it was in Isaiah's time. The cotton industry relied entirely on the flow of the Nile, first to grow the flax and then to produce the linen. All who worked to manufacture Egypt's fine linens would be unemployed. All the people—from those who comb the flax to break down the fibers to those who weave the threads together to make the rich fabrics—would lose their income.

The Lord wants Judah to understand that all of Egypt's prosperity is a gift from Him through the Nile. It is a gift that God can take away from a people who falsely believe that the idols they serve provide for them instead of the true God of Israel.