Albert Barnes Commentary Isaiah 9:21

"Manasseh, Ephraim; and Ephraim, Manasseh; and they together shall be against Judah. For all this his anger is not turned away, but his hand is stretched out still." — Isaiah 9:21 (ASV)

Manasseh, Ephraim - This verse is a continuation of the statement regarding the extent and fearfulness of the faction. Those who were previously most tenderly and intimately allied with each other would now be engaged in furious strife. Manasseh and Ephraim were the two sons of Joseph (Genesis 46:20), and their names are used as expressive of tender union and friendship . The tribes of Ephraim and Manasseh were near each other, and they always were allied. The expression here denotes that those who had previously been joined in tender alliance would be torn into contending factions, thirsting for each other’s blood.

And they together - They would be united in opposing Judah while they were devouring each other, as it is not an uncommon thing for those who are opposed to each other to unite in hostility to a common foe . This is an image that heightens the description of the anarchy—introducing implacable animosity against another tribe, while they were contending among themselves. That such anarchies and factions existed is apparent from all the history of the kingdom of Israel (Compare to 2 Kings 15:10 and following; 2 Kings 15:30). In this last passage, the death of Pekah is described as having occurred in a conspiracy formed by Hoshea.

For all this ... - See Isaiah 9:12, and the note on Isaiah 5:25. This closes the third strophe or part of the prophecy under consideration. The fourth and last strophe occurs in Isaiah 10:1-4.