Because Yahveh said this to me with the strength of the hand resting, and he instructed me against walking in the way of this people, saying, 12 “You must not call conspiracy everything that this people calls conspiracy, and you must not fear its fear, and you must not live in dread. 13 You should regard Yahveh of armies as holy, and he is the one you all should fear, and he is the one you all should dread. 14 And he will become like a sanctuary and a stumbling-stone, and like a stumbling-rock for the two houses of Israel, like a trap and a snare for the inhabitants of Jerusalem. 15 And many shall stumble among them, and they shall fall and they shall be broken, and they shall be ensnared and they shall be caught.” 16 Bind up this testimony; seal this teaching among my disciples. 17 And I will wait for Yahveh, who hides his face from the house of Jacob, and I will await him.
the one you all should fear
During World War II, president Franklin Roosevelt told the U.S.A. that the only thing we had to fear was fear itself. That was not true in the strictest sense. It was a terrible time, and everybody had lots to fear. But it was true in the sense that fear of what might happen was to prove to be a greater enemy that the ones we were fighting.
Isaiah saw all of Judah in terror over the might of Assyria, which he had just described as a mighty flooding river. But then he said that Judah needed to put their fear not on that target, but the one they should fear is God. Yes, the king of Assyria can kill you, but God can destroy you entirely, body and soul, in hell. Also, fearing the mighty Assyrian army is not the solution to the problem. Fearing God is, because it leads to national repentance and restoration by his power.
LORD, remove our fear in everyone else but you.
 Matthew 10:28.