Commentaries:
Just in case we thought it was sufficient to stand only in reverence or awe or respect of Him, Isaiah adds, "Let Him be your dread!" God is asking, in effect, "Of whom are you more afraid, the Assyrians or Me?"
In The Interpreter's Bible Commentary appears an interesting comment regarding this passage. The editors saw clearly that God was instructing Isaiah to turn away from the bulk of the Israelites and aim his message at a tiny remnant of people who were willing to be obedient and faithful in response to God. He tells the prophet to reject the main body and pay attention to a small group, the remnant that desires to be faithful to God. He said, "I will become a snare, a trap, to those who are turning away from Me. They will stumble as a result of not having the fear of God and because of their faithlessness."
God does not seem the least bit worried that His people should dread Him. Indeed, this dread, rather than hindering a proper relationship with Him, is advanced as producing a positive benefit. He becomes a sanctuary, a place of abode, to which his people can run for safety. He is a place of safety for those who fear Him!
John W. Ritenbaugh
The Fear of God
Isaiah is talking about fear. The historical background is that Judah felt threatened by the presence of the Assyrian empire. They were sweeping down and conquering all of the nearby nations. Judah was frightened. As the people of God, what should they have done? In deep respect, awe, and faith, they should have cried out to God for His protection. He is the Lord of heaven and earth. He governs it all. He could easily have stopped the Assyrians. However, the people conspired with other nations, saying to them, in effect, "You protect us. We will ally with you. We are afraid of the Assyrians, but if we join together, we will have enough power to fend them off and be safe."
God looked at that as a conspiracy against Him. He was their Lord, their King, their God. He certainly had the power to protect. And thus, His instruction to Isaiah: "Do not enter into that conspiracy with them."
John W. Ritenbaugh
The Fear of God