In this thou shalt know that I am the Lord. Pharaoh had declared on the occasion specially referred to, "I know not Jehovah, neither will I let Israel go" (Exodus 5:2). He is now told that he shall "know Jehovah" in the coming visitation; he shall know, i.
e; that there is a great and truly existent God who controls nature, does as he will even with the Nile, which the Egyptians regarded as a great deity; and can turn, if he see fit, the greatest blessings into curses.
Behold, I will smite. God here speaks of the acts of Moses and Aaron as his own acts, and of their hands as his hand, because they were mere instruments through which he worked. The Roman law said: "Qui facit per alium, tacit per se."
The waters … shall be turned to blood. Not simply, "shall be of the colour of blood," as Rosenmuller paraphrases, but shall become and be, to all intents and purposes, blood. It is idle to ask whether the water would have answered to all the modern tests, microscopic and other, by which blood is known.
The question cannot be answered. An that we are entitled to conclude from the words of the text is, that the water had all the physical appearance the look, taste, smell, texture of blood: and hence, that it was certainly not merely discoloured by the red soil of Abyssinia, nor by cryptegamic plants and infusoria.
Water thus changed would neither kill fish, nor "stink," nor be utterly undrinkable.