Isaiah returns to the prophecies he has made. There are two. The first was that Remaliah (represented by their ruler Rezin) and the Syrians will not hinder Judah. Of that prophecy Isaiah notes that while it appears bleak, it will turn out well. There might be some bricks that fall, but they will be replaced with stronger hewn stones. Judah will survive and be stronger after the first threat.
The threat will be ended, not because Judah will prevail militarily, but because Assyria will sweep them away. Assyria will devour Israel, which is the name for the northern kingdom and the location of the ten tribes. What becomes the caution in this temporarily hopeful situation is that while this favorable thing is happening, Jehovah will continue to be angry with wayward Judah. When it says that his hand is stretched out still, it is an image of a ruler who is still commanding armies to come against them. Those armies will be from Assyria.