The doctrinal importance of the virgin birth is seen in at least three areas.
1. It shows that salvation ultimately must come from the Lord. Just as God had promised that the “seed” of the woman (Gen. 3:15) would ultimately destroy the serpent, so God brought it about by his own power, not through mere human effort. The virgin birth of Christ is an unmistakable reminder that salvation can never come through human effort, but must be the work of God himself. Our salvation only comes about through the supernatural work of God, and that was evident at the very beginning of Jesus’ life when “God sent forth his Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons” (Gal. 4:4–5).
2. The virgin birth made possible the uniting of full deity and full humanity in one person. This was the means God used to send his Son (John 3:16; Gal. 4:4) into the world as a man. If we think for a moment of other possible ways in which Christ might have come to the earth, none of them would so clearly unite humanity and deity in one person. It probably would have been possible for God to create Jesus as a complete human being in heaven and send him to descend from heaven to earth without the benefit of any human parent. But then it would have been very hard for us to see how Jesus could be fully human as we are, nor would he be a part of the human race that physically descended from Adam. On the other hand, it probably would have been possible for God to have Jesus come into the world with two human parents, both a father and a mother, and with his full divine nature miraculously united to his human nature at some point early in his life. But then it would have been hard for us to understand how Jesus was fully God, since his origin was like ours in every way. When we think of these two other possibilities, it helps us to understand how God, in his wisdom, ordained a combination of human and divine influence in the birth of Christ, so that his full humanity would be evident to us from the fact of his ordinary human birth from a human mother, and his full deity would be evident from the fact of his conception in Mary’s womb by the powerful work of the Holy Spirit.
3. The virgin birth also makes possible Christ’s true humanity without inherited sin. As we noted in chapter 24, all human beings have inherited legal guilt and a corrupt moral nature from their first father, Adam (this is sometimes called “inherited sin” or “original sin”). But the fact that Jesus did not have a human father means that the line of descent from Adam is partially interrupted. Jesus did not descend from Adam in exactly the same way in which every other human being has descended from Adam. And this helps us to understand why the legal guilt and moral corruption that belongs to all other human beings did not belong to Christ.
This idea seems to be indicated in the statement of the angel Gabriel to Mary, where he says to her,
“The Holy Spirit will come upon you,
and the power of the Most High will overshadow you;
therefore the child to be born will be called holy
the Son of God.”
Because the Spirit brought about the conception of Jesus in the womb of Mary, the child was to be called “holy.” Such a conclusion should not be taken to mean that the transmission of sin comes only through the father, for Scripture nowhere makes such an assertion. It is enough for us merely to say that in this case the unbroken line of descent from Adam was interrupted, and Jesus was conceived by the power of the Holy Spirit. Luke 1:35 connects this conception by the Holy Spirit with the holiness or moral purity of Christ, and reflection on that fact allows us to understand that through the absence of a human father, Jesus was not fully descended from Adam, and that this break in the line of descent was the method God used to bring it about that Jesus was fully human yet did not share inherited sin from Adam.
But why did Jesus not inherit a sinful nature from Mary? The Roman Catholic Church answers this question by saying that Mary herself was free from sin, but Scripture nowhere teaches this, and it would not really solve the problem anyway (for why then did Mary not inherit sin from her mother?). A better solution is to say that the work of the Holy Spirit in Mary must have prevented not only the transmission of sin from Joseph (for Jesus had no human father) but also, in a miraculous way, the transmission of sin from Mary: “The Holy Spirit will come upon you … therefore the child to be born will be called holy” (Luke 1:35).
It has been common, at least in previous generations, for those who do not accept the complete truthfulness of Scripture to deny the doctrine of the virgin birth of Christ. But if our beliefs are to be governed by the statements of Scripture, then we will certainly not deny this teaching. Whether or not we could discern any aspects of doctrinal importance for this teaching, we should believe it first of all simply because Scripture affirms it. Certainly such a miracle is not too hard for the God who created the universe and everything in it—anyone who affirms that a virgin birth is “impossible” is just confessing his or her own unbelief in the God of the Bible. Yet in addition to the fact that Scripture teaches the virgin birth, we can see that it is doctrinally important, and if we are to understand the biblical teaching on the person of Christ correctly, it is important that we begin with an affirmation of this doctrine. 
 Grudem, W. A. (2004). Systematic theology: an introduction to biblical doctrine (pp. 529–532). Leicester, England; Grand Rapids, MI: Inter-Varsity Press; Zondervan Pub. House.