What does Isaiah 19:7 mean?

Faced with the threat of unstoppable foreign invaders, the tiny nation of Israel looked for help. Why not make an alliance with the strong nation of Egypt to find some protection? Isaiah's oracle (Isaiah 19:1–4) is the Lord's word to Judah about the problem with such a plan. The Lord will bring judgment on Egypt that will leave them powerless. Judah must trust God alone to save them. Not only will Egypt become powerless because of internal division and external invasion, the Lord will dry up the lifeblood of the nation: the mighty Nile River (Isaiah 19:5–6).

Egypt was entirely dependent on the Nile for food, travel, and its economy. The river did much more than carry water to the desert. It was also predictable enough to anchor an entire civilization. On nearly the same week every year, the river would flood in lower Egypt. This flood would turn miles and miles of dry land into a shallow sea. Then, again with predictable timing, the waters would recede. The newly uncovered soil was rich and fertile: ideal for crops. It was such a predictable process that the Egyptians could easily become complacent about the annual abundance the river would provide. They were completely unprepared when that abundance didn't arrive.

The Lord declares to Judah that He will dry up the Nile. He would create empty spots of desert along its banks where abundant vegetation once grew. Everything around it will become a parched, dry wilderness. This situation parallels what happened during the life of Jospeh (Genesis 41:1–4; 28–31) when a sever famine occurred, likely caused by a drought that interrupted the Nile's typical cycle.