The Nile River was the Egyptians' sole source of water, and they worshiped it as a god. After all, without the Nile there would be no bread to eat and no life-sustaining blood coursing through their veins.

G‑d, however, was sending them a message: "It is not the Nile that nourishes you. It is I who gives you life. Proof is that if I turn the water to blood, bypassing the process that I have put in place, not only will the Nile not give you life, it will make you ill."

It is not my job, my hard work, or my unique talents that give me life, but G‑d, who in His kindness orchestrates things just so that I may sustain myself.