Commentators explain this plague was a direct assault on Egyptian religion. The Nile was worshipped as a god, Hapi. By turning their source of life and worship into blood, God demonstrated His supreme power over their false gods. As Matthew Henry notes, "Whatever creature we idolize, God justly takes from us or makes bitter to us." It was also a righteous punishment for the Egyptians having stained the same river with the blood of Hebrew infants.