Good Grief! Did you actually read the whole story?
The child was NOT to be born to Ahaz!
The word "almah" is an old discussion. Get to the meat of the story.
Isaiah 7:14 (Tanakh)
Therefore the Lord Himself shall give you a sign: behold, the young woman shall conceive, and bear a son, and shall call his name Immanuel.
Matthew 1:23 (NIV)
"Behold, The virgin shall be with child and shall bear a son, and they shall call his name Immanuel," which translated means, "God with us.
Now both verses say they shall call his name Immanuel, but when we read these verses:
Isaiah 8:3 (Tanakh)
And I went unto the prophetess; and she conceived, and bore a son. Then said the LORD unto me: 'Call his name Maher-shalal-hashbaz.
Matthew 1:21 (NIV)
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.
God didn't say to name the child Immanuel.
Think about it. They shall call his name Immanuel, which means God is with us.
Isaiah 8:8, 10 (Tanakh)
...And he shall sweep through Judah overflowing as he passeth through he shall reach even to the neck; and the stretching out of his wings shall fill the breadth of thy land, O Immanuel....propose your plan, but it will not for God is with us.
Since God had Isaiah name his child Maher-shalal-hashbaz, God did not intend the child to be named Immanuel; and since God had Joseph name his son Jesus, God did not intend for him to be named Immanuel.
So what is the point of Immanuel?
IMO, it is someone or group calling out "God is with us."
The NT does not show us that this phrase was uttered by anyone during the life of Jesus.
As I pointed out earlier, the rest of the sign for Ahaz, or House of David if you prefer, does not point to Jesus or a messiah in the distant future.
A gentle answer turns away wrath, But a harsh word stirs up anger.