Thus saith the Lord, in this thou shalt know that I am the Lord,.... By the following instance of his power and vengeance: behold, I will smite with the rod that is in my hand; which though in the hand of Moses, Exo 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.