Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel." -Isaiah 7:14
In the Old Testament, it was prophesied that the Messiah will be born of a Virgin. The New Testament claims that Jesus was both Divine and Human, also known as the God-Man/the Incarnation. Therefore Jesus had to be born miraculously. His humanity was established so that He could die for mankind. His divinity was important so that His sacrifice would have divine value and would be sufficient to atone for the sins of mankind. As defined in the Old Testament, a sacrifice to God had to be without blemish.
"This is the ordinance of the law which the LORD has commanded, saying: ‘Speak to the children of Israel, that they bring you a red heifer without blemish, in which there is no defect and on which a yoke has never come." - Numbers 19:2
"You shall not sacrifice to the LORD your God a bull or sheep which has any blemish or defect, for that is an abomination to the LORD your God." - Deuteronomy 17:1
Therefore He could not be born from a purely human lineage because then he would have a sin nature, hence the Virgin Birth was a miraculous intervention implemented by the Holy Spirit who overshadowed Mary.
"But while he thought about these things, behold, an angel of the Lord appeared to him in a dream, saying, “Joseph, son of David, do not be afraid to take to you Mary your wife, for that which is conceived in her is of the Holy Spirit." - Matthew 1:20