Charles Ellicott Commentary Isaiah 31:9

"And his rock shall pass away by reason of terror, and his princes shall be dismayed at the ensign, saith Jehovah, whose fire is in Zion, and his furnace in Jerusalem." — Isaiah 31:9 (ASV)

He shall pass over to his strong hold for fear. —Most recent critics translate, His rock will pass away for terror, the “rock” (not the same word, however, as that elsewhere, e.g., Deuteronomy 32:31, used for God) being the symbol of Assyria’s strength. The laws of parallelism point to our taking the noun as the subject of the sentence, corresponding to “princes” in the next clause, and so exclude the Authorized Version.

Whose fire is in Zion. —Fire, as the symbol of the Divine glory, giving light and warmth to the faithful, and burning up the evil. (Compare Isaiah 10:16-17.)