Albert Barnes Commentary Jeremiah 46:13

"The word that Jehovah spake to Jeremiah the prophet, how that Nebuchadrezzar king of Babylon should come and smite the land of Egypt." — Jeremiah 46:13 (ASV)

A new prophecy, foretelling the successful invasion of Egypt by Nebuchadnezzar, has been appended to the hymn of triumph, because they both relate to the same kingdom. This prophecy was probably spoken in Egypt to warn the Jews there, that the country which they were so obstinately determined to make their refuge would share the fate of their native land.

How ... should come— Or, concerning the coming “of Nebuchadrezzar.”