Chapter seven records the backstory of the invasion of Israel and Syria against Judah that is recorded in 2 Kings 16. If this took place shortly after Ahaz became king, as 2 Kings implies, then it was 732 B.C., eight years after Isaiah’s commissioning in chapter six and only ten years before Assyria invaded Israel. When Ahaz heard that Israel and Syria were trying to end his new reign, he planned to ask Assyria for help. However, God sent Isaiah to Ahaz with the message that he would not be defeated, because his enemies were basically burned out; they no longer had the strength they thought they had. However, God said that Ahaz and his court (the “you” in verse nine is plural, probably the other government officials) had to believe in God in order to “remain secure.”
In case Ahaz found it hard to believe Isaiah, God offered him “a confirming sign” – any sign, even something from the depths of the Earth or in the heavens (Isaiah 7:10-17). With feign spirituality Ahaz said that he would not think of testing God, but he did not realize that God intended to give him one anyway. Isaiah 7:14 is the famous prophecy that Matthew quoted (Matthew 1:23) as being fulfilled by Jesus. However, there must have also been a near fulfillment in order for it to be a sign for them (“you” is plural again). A young woman would conceive and bear a son (something that no one can really control) and call him “Immanuel.” This was probably due to the fact that the prophecy had come true, showing that God was still present with them in their situation. The young child would grow up on “sour milk and honey,” representing a period of prosperity in Judah (“abundance of milk,” Isaiah 7:22). The ability to “know how to reject evil and choose what is right” indicates maturity, possibly bar mitzvah age. Thus, before the young man was 12-13 years old, both Israel and Syria would be “desolate,” which is exactly what happened. God used Egypt and Assyria to take them out. Unfortunately, Ahaz did not believe Isaiah and asked Assyria for help anyway (2 Kings 16), so God’s message of deliverance became one of judgment, and Judah ended up experiencing the same fate as Israel.