Albert Barnes Commentary Isaiah 9:9

"And all the people shall know, [even] Ephraim and the inhabitant of Samaria, that say in pride and in stoutness of heart," — Isaiah 9:9 (ASV)

And all the people shall know - Shall know the message; or shall know the judgment which God denounces against their crimes. The Chaldee renders this, ‘All the people have exalted themselves, Ephraim and the inhabitants of Samaria, in their magnitude, and in the pride of the heart.’

Ephraim - This is another name for Israel, as Ephraim was the principal tribe .

And the inhabitants of Samaria - The capital of Ephraim or Israel .

That say in the pride - This is a description of general and prevalent pride; and it is traced to the source of all pride—the heart. It was a desire for splendor, power, and magnificence, originating in the heart, and manifesting itself by the language of self-confidence and defiance of the judgments of God.

Stoutness - Hebrew ‘Greatness.’ It means a self-confident purpose; and indicates the state of feeling in a man when he trusts in his own resources, and not in God.