The rod that is in my hand, i.e., "in the hand of my servant." God is here represented as about to do that which was actually done by Aaron (Exodus 7:20). "Qui facit per alium, facit per se."
behold, I will smite with the rod that is in my hand; which though in the hand of Moses, Exodus 7:18 yet he being his ambassador, and representing him, is said to be in the hand of the Lord; and with this he threatens to smite
upon the waters which are in the river; the river Nile, and the canals thereof:
and they shall be turned to blood; and if this river was their god, it would abundantly appear that the God of the Hebrews was Jehovah, and above all gods, and particularly above theirs.