Isaiah poetically defines the burning of Israel. In verse 25, he notes that Jehovah continues with his righteous anger. That his hand is stretched out still refers to his destructive anger. In that righteous anger, the Lord will use other nations of the earth to exact his judgment upon Israel.
Thus, Jehovah calls the nations from afar. In this case, Assyria, but in prophetic language for the children of Lehi, the Babylonians. The coming armies will be strong and powerful, not sleeping, but enacting destruction. The result will be darkness and sorrow upon the land.
This ends a chapter in the original Book of Mormon. While it appears gloomy, we should remember the image of the fields which return after the burning of the stubble. That hope remains, even if not specifically stated.