As is the common theme with prophets, the solution to the people’s problems come through returning to their God. Isaiah is told to preach boldly. To those who think that a confederacy will save them, he tells them that it will not. Nevertheless, they should not be afraid.
The solution is to turn to Jehovah: “and let him be your fear, and let him be your dread.” In other words, do not fear man. Do not even fear the mighty Assyrians, but fear Jehovah who is even more mighty. In the Old Testament, the use of the word fear is often not intended as a synonym for being afraid, but rather being in awe. It describes the relationship of mortal humankind to their powerful God. Thus, the people are being told to return to the respect and worship of Jehovah.
If they do so, “he shall be for a sanctuary” for the faithful children of Israel, but a stumbling-block for those who do not return to Jehovah’s proper way.