The Virgin Birth tells us who Jesus is

It had to be a virgin to whom Christ came, for if it were a normal conception, he would have been a normal man, begotten of a man; but he is eternally begotten of the Father, God of God, and therefore he is God; and he must be God, so that he would be able to save us (so Arius was wrong). And he did not merely borrow her womb, but took of her flesh to bind himself to our race; and he must be man, in order to be the Savior of men (so the docetists were wrong). And he is man in order truly to suffer, and that his suffering might be as man, for man; and he is God in order that he might raise himself from the dead on the third day and so bring us victory over the grave. There is no more wondrous and mysterious thing to ponder than the blessed reality of the incarnation. Sermon for Advent II midweek, on St. Luke 1:26-38.