(Isa. 7:4)
The designation of the two kings as “the two tails of these smoking firebrands” also carries meaning. A firebrand was a torch. The description of these two kings as tails which are smoking indicates that their strength had been spent, as a torch smokes only when it is burned out.
(Monte S. Nyman, Great Are the Words of Isaiah [Salt Lake City: Bookcraft, 1980], 55.)
Isaiah was telling Ahaz to abandon his plans to arm the Jews and prepare a defense. Isaiah was also instructed to assure Ahaz that he had nothing to fear from these two kings from the north. The Lord compared their threat to the “tails of … smoking firebrands.” A firebrand is a burning piece of wood, or a torch. When it has served its purpose and burned out, it becomes nothing but a “smoking firebrand” with little trails of smoke rising from its spent ashes. The Lord knew that both Ephraim (or the Ten Tribes under Ephraim) and Syria were soon to be conquered by the Assyrians, and that if Judah would simply “be quiet” and not provoke these northern enemies, their threatened attack on Judah would be aborted because they themselves would be under attack from Assyria.”
(W. Cleon Skousen, Isaiah Speaks to Modern Times, [Salt Lake City: Ensign Publishing Co., 1984], 201.)