Charles Spurgeon 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)

And say to him,

The prophet is told the word he is to speak as well as the place where he is to deliver the message. Isaiah knew that he was soon to go and deal with men of hard heart and deaf ear. The other day we read the sixth chapter of this prophecy; and we noted the hard task that Isaiah had to perform. Now he is beginning his work with the man whom the Bible calls, "That king Ahaz," as if it could not say anything bad enough of him, but had merely to mention his name, and everybody would know who was meant.

Take heed, and be quiet; fear not, neither be fainthearted for the two tails of these smoking firebrands, for the fierce anger of Rezin with Syria, and of the son of Remaliah.

Their kingdoms were dying out. They were like burnt-out firebrands; they made a little smoke, but within a very short time there would be nothing left of them, and Ahaz need not be afraid of them.