The prophet now changed his perspective as well as his figure. Even though Assyria would menace and, indeed, destroy Jerusalem, Yahweh of armies would cut the enemy down to size as a lumberjack trimmed branches off a tree and finally felled it. God"s irresistible instrument would cut back Assyria"s many lofty leaders. This would be a felling as colossal as the harvesting of Lebanon"s vast forests (cf. Ezekiel 31:3). [source][source][source]
"The . . . "forest thickets" refers to thick underbrush that must be cleared to allow the fine trees to grow. ..."the Lebanon" refers, not to a country as today, but to a region on the slopes of Mount Hermon to the north of Israel. It was renowned for the magnificent gigantic trees which grew there." [1][source]
This prophecy found literal fulfillment when God Himself defeated the Assyrians in605 B.C. (ch37). [source][source][source]