Why do the plagues begin with the river? Why does God begin with the Nile? Well, we know from a lot of sources from this period of time in Egyptian life, that the ancient Egyptians looked upon the Nile as the primary source of their existence. We have quotes from Greek historians and others who will say things like this. "All know that Egypt is the Nile, and the Nile is Egypt." The Egyptians saw the Nile as the source of all their prosperity; and of all the richness of their soil and their growing capacities and, in fact, they even thought the Nile to be divine. And so the plagues begin with the Nile, and as they do so, we see the Lord striking at the very heart of Egypt's existence. It's that place that Egypt would feel it most keenly.
Ligon Duncan