Albert Barnes Commentary Isaiah 10:34

"And he will cut down the thickets of the forest with iron, and Lebanon shall fall by a mighty one." — Isaiah 10:34 (ASV)

And he shall cut down the thickets of the forest - The army of the Assyrians, described here as a thick, dense forest; compare Isaiah 10:18-19.

With iron - As a forest is cut down with an axe, so the prophet uses this phrase here, to keep up and carry out the figure. The army was destroyed with the pestilence (2 Kings 19:35); but it fell as certainly as a forest falls before the axe.

And Lebanon - Lebanon is here evidently descriptive of the army of the Assyrian, retaining the idea of a beautiful and magnificent forest. Thus, in Ezekiel 31:3, it is said, the king of the Assyrians was a cedar of Lebanon with fair branches. Lebanon is usually applied to the Jews as descriptive of them (Jeremiah 22:6; Jeremiah 22:23; Zechariah 10:10; Zechariah 11:1), but it is evidently applied here to the Assyrian army; and the sense is, that that army should be soon and certainly destroyed, and that, therefore, the inhabitants of Jerusalem had no cause of alarm; see the notes at Isaiah 37.