shall know: i.e. by. great experience. That was the great object of all these ten plagues; as it will be in the coming day of the judgments described in the Apocalypse. Revelation 16:5-7.
Related Commentaries of Exodus 7:5
Exodus 7:5
5 And the Egyptians shall know that I am the LORD, when I stretch forth mine hand upon Egypt, and bring out the children of Israel from among them.