Both Matthew and Luke attest to the virgin birth of Christ."... behold, an angel of the Lord appeared to him in a dream, saying, 'Joseph, son of David, do not be afraid to take Mary as your wife; for the Child who has been conceived in her is of the Holy Spirit. She will bear a Son; and you shall call His name Jesus, for He will save His people from their sins.' Now all this took place to fulfill what was spoken by the Lord through the prophet: '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.' (Matt 1:20-23)"
"The angel said to her, 'Do not be afraid, Mary; for you have found favor with God. And behold, you will conceive in your womb and bear a son, and you shall name Him Jesus. ... and the Lord God will give Him the throne of His father David; ... and His kingdom will have no end.' Mary said to the angel, 'How can this be, since I am a virgin?' The angel answered and said to her, 'The Holy Spirit will come upon you, and the power of the Most High will overshadow you; and for that reason the holy Child shall be called the Son of God.' (Luke 1:30-35)"
Is there something significant about this beyond Isaiah's prophecy? There are several important factors connected to the virgin birth.
1. Presence. He will be called "Imanu-El" which means "God is with us." God could have chosen a person to endow with great power and insight to turn the people back to God. However, a prophet could not save the people from their sins. A prophet could not bring God's presence to the people.
2. Relationship. The child would be called the "Son of God." This was a typical title for kings. However, the way Jesus uses this phrase in his ministry shows that it is much more than this (John 3:16; 5:19-23; 8:42; 10:30). "Son of God" is also about the relationship between God and Jesus. Only Jesus is uniquely God's son. So Jesus has a special relationship to God that no one else has.
But Jesus often called himself the "Son of Man," which is a Hebrew phrase that simply means, "human" as opposed to "divine." Jesus was human because he was "born of a woman (Gal 4:4)." John expresses it as Jesus becoming "flesh (John 1:14)." John affirms this as a cardinal doctrine (1 Jn 4:2).
However, he was also born of the Holy Spirit according to the infancy narratives. Jesus was a man, and also God. "For in Him all the fullness of Deity dwells in bodily form (Col 2:9)." So all the fullness of God existed in Jesus as well as the fullness of humanity. This is why there had to be a virgin birth. If there is no virgin birth, then Jesus is only a Son of Man, but not the Son of God.
So, not only does Jesus bear a unique relationship to God, he also bears a relationship to humanity.