At the time God did this, He would darken the skies over Egypt so the light of the sun, moon, and stars would not shine on the land (cf. Joel 2:10; Joel 2:31; Revelation 8:12-13). This announcement recalls the plague of darkness that the Lord sent before the Exodus ( Exodus 10:21-23). He would again humiliate the gods that the Egyptians credited with bringing light and providing life. [source][source][source]
"The overthrow of Egypt was a prelude [1], as it were, to the destruction of world rule in the last days." [2][source]