Why it shall come to pass, that when the Lord has performed his whole work on mount Zion and on Jerusalem…
The "stout heart" here threatened is entirely different from true magnanimity or greatness of mind, arising from good principles and accompanied with other virtues, which excites to the most laudable and renowned actions. It is an odious, stubborn disposition, which acts in direct contrariety to lowliness of mind and poverty of spirit, whereby people are inclined to think modestly of their abilities and performances; it proceeds from pride, is strengthened by external grandeur and dignity, and discovered by vain self-conceit and foolish boasting of past exertions and successes, and future intended enterprises. The fruit of the king of Assyria's stout heart was a daring expedition against Jerusalem, undertaken in proud contempt of the true God, and accompanied with blasphemous insults, repeatedly offered to the Most High over all the earth.
Parallel VersesKJV: 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.
WEB: Therefore it will happen that, when the Lord has performed his whole work on Mount Zion and on Jerusalem, I will punish the fruit of the willful proud heart of the king of Assyria, and the insolence of his haughty looks.