(Read Isaiah 7:10-16)

Secret disaffection to God is often disguised with the colour of respect to him; and those who are resolved that they will not trust God, yet pretend they will not tempt him. The prophet reproved Ahaz and his court, for the little value they had for Divine revelation. Nothing is more grievous to God than distrust, but the unbelief of man shall not make the promise of God of no effect; the Lord himself shall give a sign. How great soever your distress and danger, of you the Messiah is to be born, and you cannot be destroyed while that blessing is in you. It shall be brought to pass in a glorious manner; and the strongest consolations in time of trouble are derived from Christ, our relation to him, our interest in him, our expectations of him and from him. He would grow up like other children, by the use of the diet of those countries; but he would, unlike other children, uniformly refuse the evil and choose the good. And although his birth would be by the power of the Holy Ghost, yet he should not be fed with angels’ food. Then follows a sign of the speedy destruction of the princes, now a terror to Judah. “Before this child,” so it may be read; “this child which I have now in my arms,” (Shear-jashub, the prophet’s own son, verse 3,) shall be three or four years older, these enemies’ forces shall be forsaken of both their kings. The prophecy is so solemn, the sign is so marked, as given by God himself after Ahaz rejected the offer, that it must have raised hopes far beyond what the present occasion suggested. And, if the prospect of the coming of the Divine Saviour was a never-failing support to the hopes of ancient believers, what cause have we to be thankful that the Word was made flesh! May we trust in and love Him, and copy his example.

For a more detailed summary select the link below.
Isaiah 7 Bible Commentary – Matthew Henry (concise) (christianity.com)

Isaiah 7:14
14 Therefore the Lord himself will give you a sign. Behold, the virgin will conceive, and bear a son, and shall call his name Immanuel.