The reason that the Lord continues to be angry with the people of Judah is that they have turned from the Lord. Isaiah has noted this several times, and emphasizes it yet again. They do not turn to Jehovah or seek him. Therefore, Jehovah will smite them.
Verse 14 says that “the Lord cut off from Israel head and tail, branch and rush in one day.” This is poetic language to encompass the vast destruction to come. The leaders as well as the laborers, and all in between, will be rapidly destroyed. That was certainly the case as Assyria swept through Judah before encamping around Jerusalem.
Verse 17 focuses on the devastation to portions of the population that would not be militarily involved. They too will feel Jehovah’s wrath. The poetic repetition comes again that his anger is not turned away, and his hand is stretched out still. It will not be over, even with those events.
In verse 18 we again have the burning. This time, it devours briers and thorns, or the wicked. There will be terrible destruction, but as with the seasonal burning of the fields, it will ultimately be a burning meant to renew. For that reason, the smoke is lifted up. This is a parallel to the incense that is offered to Jehovah in the temple. There is an ultimate divine result of this terrible devastation.