The impending prophecy shatters the false sense of security held by the Egyptian empire. It completely removes the foundation from everything Pharaoh trusted, primarily the immense size of his population. God decrees the absolute end and total annihilation of the Egyptian masses [מצודת ציון, מצודת דוד, ביאור שטיינזלץ].
This is a decree of actual, physical destruction. Unlike other nations, such as Cush, which are destined only to suffer from fear and panic without their lands being ruined, Egypt faces complete devastation. God will bring about this ruin through Nebuchadnezzar, the king of Babylon, who will strike down the multitudes of Egypt with the sword and destroy them [מלבי״ם, מצודת דוד].
Pharaoh placed his confidence in his massive numbers, his idols, his fortified cities, and his past military victories. Because of this misplaced trust, God ensures that the very masses Pharaoh relied upon will be entirely wiped out by Nebuchadnezzar and his army. This invading force arrives with a single, devastating purpose: to conquer, ruin, and utterly destroy the land [אברבנאל].