Isaiah 9:18

18. We have passed two strophes, and here enter on the third, which closes the chapter. They are apparently artificial and antiphonic. Possibly the prophet pronounced the grave causes of judgment upon judgment, and his disciple-adherents added the gloomy refrain. The scene may have occurred in the temple court, where were gathered, as by appointment, the king, nobles, false prophets and leaders, and the people. More gladly did they this time listen than if themselves were the immediate objects of the denounced judgments. They were, however, familiar enough with them as of their own deserving; and, probably, in their minds were likely to be yet more. There can be little doubt of Isaiah’s large indirect influence on the affairs of state. But Ahaz was so committed to an Assyrian policy, and so entangled by it, that the prophet’s statesmanship was less apparent in his reign; but obviously more in that of Hezekiah, his son and successor.

For wickedness Prevailing impiety and blasphemy.

Burneth as the fire Extends as fire does among thorns and thickets. Or, it smoulders, when long pent up, then bursts forth irresistibly. See Hosea 7:6. Wickedness produces its own punishment.

Briers and thorns An image, probably, of the lower grades of the population, where the fires of corruption and punishment are first seen.

Thickets of the forest Among ranks grading upward, till high and low receive the conflagration together.

Mount up like… smoke The “smoke” of their destruction ascendeth to heaven.