The Prophecy - Isaiah 7:14-16
Therefore the Lord himself will give you a sign: The young maiden (virgin) will be with child and will give birth to a son, and will call him Immanuel. He shall eat curds and honey when he knows how to refuse the evil and choose the good. For before the boy knows how to refuse the evil and choose the good, the land whose two kings you dread will be deserted.
The Fulfillment - Matthew 1:18-23
This is how the birth of Jesus the Messiah came about: His mother Mary was pledged to be married to Joseph, but before they came together, she was found to be pregnant through the Holy Spirit. Because Joseph her husband was faithful to the law, and yet did not want to expose her to public disgrace, he had in mind to divorce her quietly. But after he had considered this, an angel of the Lord appeared to him in a dream and said, “Joseph son of David, do not be afraid to take Mary home as your wife, because what is conceived in her is from the Holy Spirit. She will give birth to a son, and you are to give him the name Jesus, because he will save his people from their sins.” All this took place to fulfill what the Lord had said through the prophet: “The virgin will conceive and give birth to a son, and they will call him Immanuel (which means God with us)."
Question: Critics will question - "Why do Christians think that Isaiah 7:14 was a prophecy about the future and not something that only involved Ahaz during his lifetime? Doesn't Isaiah 7:14 only concern Isaiah and Ahaz? They will argue that verse 10-11, plainly says that the sign is to Ahaz, and verse 14 says the Lord himself shall give you (Ahaz) a sign. It's all addressed from Isaiah to Ahaz - not one thing is addressed to the future. There is no prophetic language such as the time will come when such and such happens. The greatest portion of this viewpoint comes from Orthodox Judaism (not surprisingly). That Isaiah 7:14 was direct and singularly attached to Isaiah, Ahaz, and the people of Judah 2700 years ago fits the narrative of most orthodox Jews - Jesus of Nazareth was not the Messiah, and they did not kill him 2000 years ago.
Response: In reality, there are two issues - a nation and a creation. One - The prophecy in Isaiah 7:14 indeed is directed at Ahaz, and had to be fulfilled during his lifetime for his (God's) people. This fulfillment is related directly to the sins and salvation of a single nation - ancient Judah. Two - It was also directed at the house and the lineage of David - and beyond. And could also be fulfilled long after the time of Ahaz, in fact, 700 or so years after. This fulfillment is related directly to the sins and salvation of all creation - to all who believe. Reading the scripture in the complete prophetic context of Isaiah 7 supports the view that the latter is true, that the Christian view of this prophecy is also correct.
In Isaiah 7:13, the prophet Isaiah specifically turns his attention from King Ahaz, who is a member of the house of David, and fires off a warning shot to the entire house of David.
Then Isaiah said, "Hear now, you house of David! Is it not enough to try the patience of men? Will you try the patience of my God also?
Then, speaking to the same audience in verse 14, Isaiah directs them to a coming sign from God.
Therefore the Lord himself will give you a sign: The virgin will be with child and will give birth to a son, and will call him Immanuel.
In chapter 7 the kings of Israel (Northern Kingdom) and Syria formed an alliance and attacked Jerusalem. Isaiah assured Ahaz that God would not allow this unholy alliance of terror to prevail. Although Ahaz would never ask God for a sign, God true to His promise proclaimed one for his people through the prophet Isaiah. The greatest sign of all.
"Therefore the Lord Himself will give you a sign: Behold, a virgin will be with child and bear a son, and she will call His name Immanuel. He will eat curds and honey at the time He knows enough to refuse evil and choose good. For before the boy will know enough to refuse evil and choose good, the land whose two kings you dread will be forsaken."
The "sign" that God gave to Ahaz has a two-fold function. The first has to do with a son who will be born to a virgin, whose name will be Immanuel, and who will eat "curds and honey," at the time these two kings will be disposed of. From verse 22 we know that "curds and honey" in that day was known as the food of prosperity and abundance, not of adversity. Had the siege been successful, the people of Jerusalem would have been starving. The child's birth may not have been supernatural, since the term "virgin" can also mean simply "maiden." It is therefore capable of at least two fulfillments - one for Ahaz's Judah, and the second for future generations of all peoples, all races, all colors, and all times. In the first "sign" the boy seems to have been naturally born, but nevertheless a sign to the king, not so much in his birth, but in the food which he ate at the time the two kings were dispatched.
But within this supernatural word of Isaiah was an even greater "sign." A sign in the making, a sign of future hope and deliverance, a sign yet to come. As we see now this prophecy through a "Back to the Future" lens the ultimate fulfillment comes from a literal virgin who (after an angelic visitation and message) would supernaturally conceive and bear a son, and this son would be the evidence of God's final and full deliverance of all of His people (not just Jews) once and for all. Only in the light of the miraculous birth of Immanuel - the Messiah would this "sign" be understood for what it truly was, thanks to Matthew's account (1:23).