Charles Ellicott Commentary Isaiah 7:4

"and say unto him, Take heed, and be quiet; fear not, neither let thy heart be faint, because of these two tails of smoking firebrands, for the fierce anger of Rezin and Syria, and of the son of Remaliah." — Isaiah 7:4 (ASV)

Take heed, and be quiet ... —The prophet meets the fears of the king by words of comfort. The right temper for such a time was one of calm courage, waiting on the Lord (Isaiah 30:15).

Neither be fainthearted. —Literally, let not your heart be soft.

For the two tails of these smoking firebrands. —The two powers that Ahaz dreaded were, in the prophet’s eyes, but as the stumps of two smoking torches. Their flame was nearly out. It would soon be extinguished.

The son of Remaliah. —There is a touch of scorn in the omission of the king’s name. So men spoke scornfully of Saul as the son of Kish (1 Samuel 10:11), and Saul himself of David as the son of Jesse (1 Samuel 20:30). It pointed out the fact that Pekah was after all but an upstart adventurer, who had made his way to the throne by rebellion and murder.