Charles Ellicott Commentary Isaiah 8:12

"Say ye not, A conspiracy, concerning all whereof this people shall say, A conspiracy; neither fear ye their fear, nor be in dread [thereof]." — Isaiah 8:12 (ASV)

Say you not, A confederacy ... —The words have been very differently interpreted.

1. The confederacy has been thought to be that between Syria or Ephraim, which had at first filled the people with terror, and then had seemed so powerful that men had been willing to join it (Isaiah 7:2; Isaiah 8:6).
2. Translating the word as conspiracy as in 2 Kings 17:4 —it was the word used by Athaliah when she cried, “Treason, treason!” (2 Chronicles 23:13)—interpreters have seen in it the cry of the Assyrian alliance party against the prophet and his followers, whom they accused of conspiracy against their country, such as was afterwards imputed to Jeremiah (Jeremiah 37:14).
3. Others, following a conjectural amendment of the text, have read, “You shall not call everything a holy thing which this people calls a holy thing,” and find in the words a protest against the idolatrous reverence for that which has no real holiness, analogous to the warning against soothsayers or diviners in Isaiah 8:19; or possibly an allusion to such an object of worship as the brazen serpent, which Hezekiah had destroyed by Isaiah’s advice (2 Kings 18:4).

Of these, (2) seems the most in harmony with the sequence of facts and thoughts.