According to Matthew, Jesus was born of a virgin named Mary (Matthew 1:18-23).
The story of the virgin birth forgets that a single woman necessarily lived with her father under his full authority (Numbers 30:3-5). If Mary were pregnant by someone other than Joseph (Matthew 1:18) her father would naturally conclude that she had been promiscuous and the law sentenced her to death by stoning (Deuteronomy 22:20-21).
Since Mary's pregnancy could not be hidden from prying eyes, far less in a village where everybody knows everything about the neighbours, either her father vouched for the virgin birth, exposing himself to public ridicule for the rest of his life, or the village miraculously acknowledged the wonder, raised Mary to divine status and made her instantly famous across Israel, or she would be stoned to death.
The Holy Spirit does not make a woman pregnant (Matthew 1:20) but a prophetess (2 Kings 22:11-20, Isaiah 11:2).
Jesus did not save his people from their sins (Matthew 1:21). The Lord forgives all the sins of anyone who fears him and obeys his precepts (Psalm 103) or whose spirit rejects deceit (Psalm 32:1-2) or who humbles himself, prays and turns from his wicked ways (2 Chronicles 7:14, Jeremiah 36:3). They who fail to comply with these conditions are not saved from their sins.
Matthew attempts to justify his yarn by resorting to Isaiah 7:14 on Matthew 1:22-23.
The context leading up to Isaiah 7:14 is that the kings of Aram and Israel made a pact of aggression against Jerusalem, and when Ahaz king of Judah first learned of it he and the nation trembled with fear.
Isaiah conveyed the first word of the Lord to Ahaz: "Keep calm, do not fear and stand firm in your faith" (Isaiah 7:1-9); but fear persisted and so the Lord sent Isaiah to the king a second time,
Again Isaiah spoke to Ahaz, "Ask the Lord your God for a sign, whether in the deepest depths or in the highest heights." But Ahaz said, "I will not ask; I will not put the Lord to the test." 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? 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. He will eat curds and honey when he knows enough to reject the wrong and choose the right. But before the boy knows enough to reject the wrong and choose the right, the land of the two kings you dread will be laid waste."(Isaiah 7:10-16. Underlined word mine)
Isaiah 7:13-14 tab who would witness the sign: the house of Israel synchronous with the monarchy of Ahaz.
Isaiah 7:15-16 provide a timeframe. The child born of the "virgin" would still be a minor when Aram and Israel were to be laid waste. This occurred about the year 730 BC (see also Isaiah 8:1-4).
These other verses in the Book of Isaiah seal the identity of Immanuel,
The Lord spoke to me again: "Because this people has rejected the gently flowing waters of Shiloah and rejoices over Rezin and the son of Remaliah, therefore the Lord is about to bring against them the mighty floodwaters of the River—the king of Assyria with all his pomp. It will overflow all its channels, run over all its banks and sweep on into Judah, swirling over it, passing through it and reaching up to the neck. Its outspread wings will cover the breadth of your land, O Immanuel!"(Isaiah 8:5-8)
Immanuel the child grew up to be Hezekiah the king because Assyria invaded the land of Judah during his reign.
The "virgin" turned out to be not a woman! but the "Virgin Daughter of Zion," an expression coined by Isaiah himself (2 Kings 19:20-21, Isaiah 37:21-22) to tag that portion of the house of Israel which remained faithful to the Lord and did not apostasize.
The byword Immanuel (lit. "God with us") took effect when the angel of the Lord eradicated Sennacherib's army (2 Kings 19:35-36, Isaiah 37:36-37) for after that event many Jebusites must have greeted one another and King Hezekiah with the cheery word, "God is with us!"
Golden Rule: If an intended Old Testament justification is fraudulent, the New Testament anecdote is a fabrication.