Exodus 7:5 - Ellicott's Commentary On The Whole Bible

The Egyptians shall know that I am the Lord. — Heb., that I am Jehovah: i.e., that I answer to my name — that I am the only really existing God, their so-called gods being “vapour, smoke, nothingness.” No doubt this was one of the main lessons intended to be taught by the whole series of miraculous events connected with the Exodus. Egypt was the greatest monarchy in the whole world. She was now at the height of her glory. Among existent polytheisms, hers was the most famous; and her gods must have seemed, not only to herself, but to all the surrounding nations, the most powerful. To discredit them was to throw discredit upon polytheism generally, and to exalt the name of Jehovah above that of all the deities of the nations. (Comp. Exodus 14:11-16.)