Charles Ellicott Commentary Exodus 7:5

"And the Egyptians shall know that I am Jehovah, when I stretch forth my hand upon Egypt, and bring out the children of Israel from among them." — Exodus 7:5 (ASV)

The Egyptians shall know that I am the Lord. — In Hebrew, that I am Jehovah: that is, that I answer to my name—that I am the only truly existing God, their so-called gods being “vapor, 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 then at the height of her glory. Among existing polytheisms, hers was the most famous; and her gods must have seemed, not only to herself but also 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 .