Last post we looked at how the prophecy of the virgin birth is in accordance with the Jewish view of all prophecy being Messianic. Now for a look at this question: Why a virgin birth?
Some anti-Christian diatribes have long insisted that the virgin birth was taught because either God or his followers are anti-sex. That's a strange accusation considering the very first blessing from God to man listed in the Bible is that man should "Be fruitful and multiply." (Genesis 1:28). Orthodox Christianity has a high view of sexual intimacy and the holiness of the physical bond and the power to create new life; these are noticeably lacking in the secular view.
Here are two of the themes that the Bible itself draws out in connection with Jesus' birth:
A new creation
Since the ancient genealogies listed Adam as "son of God", none since could claim that -- until Jesus, who could likewise claim God himself as father. To the original Jewish audience, this is an echo of creation. It shows Jesus as the beginning of the new creation, of the new heavens and new earth that had been foretold. His birth announces him as the "second Adam". Paul picks up on this theme of the new creation beginning with Christ.
What of the old creation?
If Jesus is supposed to be like Adam, then why not create Jesus from the dust to be the beginning of an entirely new creation? To create from the dust would be to make a new human race. That kind of creation would be alien to humanity as it exists. This kind of "new creation" would replace the old; when the former things pass away, there would be no trace of what had gone before. But Jesus is the beginning of the new creation from within our own humanity. As Paul writes, "born of woman, born under the law, to redeem those under the law." He does not come to replace us, but to redeem us. The promise of Jesus being born of a woman, like us, is that we will likewise be transformed into this new kind of humanity -- also become "sons of God" through what Christ has done for us.