The Lord tells Ahaz, through Isaiah, not to fear the enemy. Why is the enemy likened to "the two tails of smoking firebrands?" A firebrand was a technique used to destroy the crops and vineyards of an enemy. Foxes would be taken, have some sort of torch (firebrand) tied to their tails, and then sent to run through the fields of the enemies. The foxes would scamper around starting fires everywhere they went. Therefore, the phrase 'two tails of these smoking firebrands' refers to Pekah and Rezin as destroyers. The fact that the firebrands are smoking suggests that the fire (representing their strength) has been extinguished. The phrase also carries a certain disdain. A good example of the use of firebrands is found in Judges:
'And Samson went and caught three hundred foxes, and took firebrands, and turned tail to tail, and put a firebrand in the midst between two tails.
And when he had set the brands on fire, he let [them] go into the standing corn of the Philistines, and burnt up both the shocks, and also the standing corn, with the vineyards and olives.' (Judges 15:4-5)