For the LORD spake thus to me with a strong hand, and instructed me that I should not walk in the way of this people, saying, Say ye not, A confederacy, to all them to whom this people shall say, A confederacy; neither fear ye their fear, nor be afraid. Sanctify the LORD of hosts himself; and let him be your fear, and let him be your dread. And he shall be for a sanctuary; but for a stone of stumbling and for a rock of offence to both the houses of Israel, for a gin and for a snare to the inhabitants of Jerusalem. And many among them shall stumble, and fall, and be broken, and be snared, and be taken.
Isaiah was instructed by Jehovah not to join this people in their fear of the conspiracy formed against them, but to trust Him alone. He will be as a sanctuary to all who rely on Him, but a stone of stumbling to all others.