Achaz had abandoned the Lord for Moloch, and put his trust in an alliance with Assyria; hence the conditional prophecy concerning Juda, "if you will not believe, you shall not continue".The test of belief follows immediately: "ask thee a sign of the Lord thy God, either unto the depth of hell or unto the height above".After Elath had fallen, Rasin joined his forces with those of Phacee; "Syria hath rested upon Ephraim", whereupon "his (Achaz') heart was moved, and the heart of his people, as the trees of the woods are moved with the wind".Immediate preparations must be made for a protracted siege, and Achaz is busily engaged near the upper pool from which the city received the greater part of its water supply. The prophet's commission is of an extremely consoling nature: "See thou be quiet; hear not, and let not thy heart be afraid of the two tails of these firebrands".As it is quite commonly admitted that the Divine judgment is directed not so much against the serpent as against the originator of sin, the seed of the serpent denotes the followers of the serpent, the "brood of vipers", the "generation of vipers", those whose father is the Devil, the children of evil, (Augustine).
The Hebrew Grammar of Gesenius-Kautzsch  establishes the rule: Peculiar to the Hebrew is the use of the article in order to indicate a person or thing, not yet known and not yet to be more clearly described, either as present or as to be taken into account under the contextual conditions.
Achaz hypocritically answers: "I will not ask, and I will not tempt the Lord", thus refusing to express his belief in God, and preferring his Assyrian policy.
The king prefers Assyria to God, and Assyria will come: "the Lord shall bring upon thee and upon thy people, and upon the house of thy father, days that have not come since the time of the separation of Ephraim from Juda with the king of the Assyrians." The house of David has been grievous not merely to men, but to God also by its unbelief; hence it "shall not continue", and, by an irony of Divine punishment, it will be destroyed by those very men whom it preferred to God.
the Old Testament, the New Testament, the early Christian and Jewish witnesses.
The Old Testament refers to Our Blessed Lady both in its prophecies and its types or figures.