Here are some of John Calvin’s thoughts on the marvelous prophecy of God through Isaiah in Is.7:14 – “Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.”
…Now it is certain… that this name Immanuel could not be literally applied to a mere man; and, therefore, there can be no doubt that the Prophet referred to Christ.
…The Prophet was about to give them a sign of deliverance. Why should he promise the Messiah, who was to be born five hundred years afterwards?
…Now, the matter stands thus. King Ahaz having rejected the sign which God had offered to him, the Prophet reminds him of the foundation of the covenant, which even the ungodly did not venture openly to reject. The Messiah must be born; and this was expected by all, because the salvation of the whole nation depended on it. The Prophet, therefore, …argues in this manner: ‘By rejecting the promise, thou wouldest endeavor to overturn the decree of God; but it shall remain inviolable, and thy treachery and ingratitude will not hinder God from being continually the Deliverer of his people; for he will at length raise up his Messiah.’
…We must attend to the custom of the Prophets, who, in establishing special promises, lay down this as the foundation, that God will send a Redeemer. On this general foundation God everywhere builds all the special promises which he makes to his people; and certainly every one who expects aid and assistance from him must be convinced of his fatherly love. And how could he be reconciled to us but through Christ, in whom he has freely adopted the elect, and continues to pardon them to the end? Hence comes that saying of Paul, that all the promises of God in Christ are Yea and Amen. (2 Cor.i.20.)
Whenever, therefore, God assisted his ancient people, he at the same time reconciled them to himself through Christ. …For on what did the deliverance of Jerusalem depend, but on the manifestation of Christ? This was, indeed, the only foundation on which the salvation of the Church always rested (Commentary on Isaiah, pp.245-46 – Baker reprint, 1979)