Isaiah speaks of the army of Assyria as if it were the tall trees in Lebanon. God will destroy the army like people cutting down the mighty trees of Lebanon. This emphasizes that though the army is strong, God has the power to destroy it. (See: [[rc://en/ta/man/translate/figs-metaphor]])
"will cut off the big branches of the trees." In order to make it clear that this refers to the army of Assyria, it can be translated as a simile: He will destroy the army of Assyria like strong men cutting off the big branches of trees. (See: [[rc://en/ta/man/translate/figs-metaphor]])
This can be reworded so that the abstract noun "crash" is expressed as the verb "make a noise." AT: "and the branches will crash down on the ground and make a terrifying noise" or "and the branches will fall to the ground with a very loud noise" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
"the dense shrubs in the forest." This is possibly a metaphor for those people who are not well known. (See: [[rc://en/ta/man/translate/figs-metaphor]])
"the forests of Lebanon will no longer be so grand." This is possibly a metaphor for the Assyrian army. AT: "Yahweh will defeat the army of Assyria, as mighty as it is" (See: [[rc://en/ta/man/translate/figs-metaphor]])