Matt 1:22-23 - All this took place to fulfill what the Lord had said through the prophet: "The virgin will be with child and will give birth to a son, and they will call him Immanuel"-which means, "God with us."
Isa. 7:14 - “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.”
To be a perfect sacrifice, Jesus must Himself be perfect -without sin. Since our race is contaminated with sin, a miraculous entrance into the world would be required, hence the virgin birth.