First, it is highlighting the essentially supernatural character of Jesus and the gospel. Alluding to Barth again, the virgin birth is posted on guard at the door of the mystery of Christmas; and none of us must think of hurrying past it. It stands on the threshold of the New Testament, blatantly supernatural, defying our rationalism, informing us that all that follows belongs to the same order as itself and that if we find it offensive there is no point in proceeding further. If our faith staggers at the virgin birth what is it going to make of the feeding of the five thousand, the stilling of the tempest, the raising of Lazarus, the transfiguration, the resurrection and, above all, the astonishing self-consciousness of Jesus? The virgin birth is God’s gracious declaration, at the very outset of the gospel, that the act of faith is a legitimate sacrificium intellectus. ‘It eliminates’, writes Barth, ‘ the last surviving possibility of understanding the vere deus vere homo intellectually. It leaves only the spiritual understanding, that is the understanding in which God’s own work is seen in God’s own light.’
Secondly, the virgin birth is a sign of God’s judgment on human nature. The race needs a redeemer, but cannot itself produce one: not by its own decision or desire, not by the processes of education and civilization, not as a precipitate of its own evolution. The redeemer must come from outside. Here, as elsewhere, ‘all things are of God’. He provides the lamb (Gn. 22:8). Barth is exactly right: ‘Human nature possesses no capacity for becoming the human nature of Jesus Christ.’
Thirdly, the virgin birth is a sign that Jesus Christ is a new beginning. He is not a development from anything that has gone before. He is a divine intrusion: the last, great, culminating eruption of the power of God in the plight of man: ‘Man is involved only in the form of non-willing, non-achieving, non-creative, non-sovereign man, only in the form of man who can merely receive, merely be ready, merely let something be done to and with himself.’
Donald Macleod, The Person of Christ, 37.