Isaiah 8:12

A confederacy Strictly: A conspiracy (R.V.). But the word "conspiracy" does not necessarily imply (as some have thought) treason within the state. It may be used (as the verb is in Nehemiah 4:2) of an external coalition threatening the integrity of the commonwealth. On the whole this seems to give the best sense here. The "conspiracy" is the Syro-Ephraimitish alliance, which Isaiah and his adherents are warned not to treat as a serious danger. Another explanation is that Isaiah and his party were suspected of treasonable complicity in the designs of the allies (cf. Jeremiah 37:13); but did they need a supernatural revelation to tell them that that charge was false? The word has also been supposed to allude to the spirit of preternatural suspicion that was abroad, causing every man to suspect his neighbour of being a traitor. But Isaiah is little likely to have been disturbed by this.

neither fear ye their fear i.e. "fear not what they fear," but fear Jehovah alone (Isaiah 8:13).