It is important for at least three reasons:
First, it was prophesied in the Old Testament Scriptures.
Isa 7:14 "Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel.
It would have broken the truthfulness of God's Word if He was not born of a virgin.
Second, it was to protect Him from inheriting fallen man's sinful nature.
The sinful nature is passed from parents to children. If His birth was the result of a union of a fallen man and a fallen woman, then He would have been contaminated by sin. His conception and birth was not the result of a union of a sperm cell and an egg cell. Mary's womb was simply the vessel or container of a baby who was miraculously conceived in the womb.
Thus, He could be humanity's Savior and new Representative Head.
Third, it was to preserve and protect His kingship.
The Messiah to be born was to be the King of Israel. Mary's genealogy can be traced to the line of kings that was qualified to inherit the throne. On the other hand, Joseph, His stepdad, in His humanity, belonged to a line that was disqualified to inherit it.
Joseph belonged to the line of Coniah. His line was disqualified from inheriting the throne. See Jer. 22:24-30 and Matthew 1:12.
Matthew is the genealogy of Joseph. Luke's is that of Mary. Both came from a royal line with Joseph's line disqualified. However, Mary's was not. Joseph was only His stepdad, while Mary was His biological mother.
If He was not virgin born, if He was the product of the union between Joseph and Mary, He would have been disqualified as king.
