Take heed - Hebrew ‘Keep thyself;’ that is, from fear.
Neither be fainthearted - Hebrew, ‘Let not thy heart be tender;’ that is, let it not be easily moved; be strong, fearless.
For the tails ... - There is much beauty and force in this comparison. The “design” of Isaiah is to diminish the fear of Ahaz. Instead, therefore, of calling them “firebrands” - burning and setting on fire everything in their way - he calls them the “tails, that is, the ends,” or remains of firebrand - almost consumed themselves, and harmless. And instead of saying that they were “burning and blazing,” he says that they were merely “smoking” - the half-burned, decaying remains of what might have been once formidable. The prophet also is just about to announce their approaching destruction by the Assyrians; see Isaiah 7:8. He, therefore, speaks of them as already almost extinguished, and incapable of doing extensive injury.
Son of Remaliah - Pekah, Isaiah 7:1. ‘It is by way of contempt that the king of Israel is not called by his own name. The Hebrews and Arabians, when they wish to speak reproachfully of anyone, omit his proper name and call him merely the son of this or that, especially when his father is but little known or respected. So Saul names David, in contempt, the son of Jesse; 1 Samuel 20:27, 1 Samuel 20:31.’ - “Hengstenberg.”