Ezekiel 32:15

“When I make the land of Egypt desolate and waste, a land destitute of its fullness, when I smite all those who dwell in it, then will they know that I am Yahweh.”

For millenniums the Egyptians had ignored Yahweh, even though they had had every chance to know Him through men like Abraham, Joseph and Moses. But they had mocked at Yahweh, and had turned His people from Him. Now they would learn Who and What He is by hard experience, as they had done under Moses (Exodus 7:5; Exodus 7:17; Exodus 8:22; Exodus 14:4; Exodus 14:18), even though they would not finally accept it. To hear of the living God and to ignore Him is the greatest of sins, and they had committed it.