Charles Ellicott Commentary Isaiah 10:12

"Wherefore it shall come to pass, that, when the Lord hath performed his whole work upon mount Zion and on Jerusalem, I will punish the fruit of the stout heart of the king of Assyria, and the glory of his high looks." — Isaiah 10:12 (ASV)

Wherefore it shall come to pass ... —Better, And it shall come to pass ... The boast of the proud king is interrupted by the reassertion of the fact that he is only an instrument in the hand of Jehovah, and that when his work was done he too will be punished for his pride. The “fruit” of the “stout heart” includes all the words and acts in which his arrogance had shown itself.