This may be partly because Christian faith has deeper roots in our midst than many care to acknowledge, but thoughtful Christians know that genuine faith rarely comes easily and that much of this amiable popularity could derive from misunderstanding and misuse. Their suspicions are intensified by the ironic realisation that few New Testament passages offer more difficulties to honest enquiries than the Christmas stories. They are found only in two Gospels, not mentioned by Paul and ignored in the first sermon in the Acts of the Apostles. What presents the greatest difficulty of all, the story that Jesus was born without the agency of a human father, receives little public discussion. Either it is accepted - or rejected - as yet another miracle, or it is dismissed as a naively pious legend.
Both attitudes are over-simplified and the matter needs more attention. Nowhere is the mystery inherent in human existence more baffling than in the circumstances of ordinary human birth. If any two parents had not met and had intercourse at that particular time, and if one among innumerable genetic possibilities had not occurred in fertilisation, then I would not have been I, nor you you. Surely this apparent fortuitousness, even in the most stable of marriages, sharpens the question of whether life as a whole is not a matter of meaningless chance?
The Nativity stories as a whole insist that, on the contrary, this particular birth was anything but a matter of chance. As Mary sang in her Magnificat, it was the fulfilment of God's long-standing covenant with Israel, and it explains otherwise puzzling parts of the story - like the long lists of begats, the account of John the Baptist's birth and the awkward winter journey to the city of David for the birth itself.
Until his public ministry began, Jesus was apparently not considered to be different from anyone else. 'Is not this the carpenter?' It was surely only with hindsight that the evangelists could have come to believe in anything special about his birth. It was not the later Nativity stories, but their knowledge of the meaning of Jesus's life, rejection, death and victory over death, as it had come to them in their own new birth in the Holy Spirit, which enabled them to dare to conclude that that same Spirit must have been uniquely present in Jesus's birth as a human being. It is hard for us to realise how immensely daring that conclusion was. As members of Israel, they knew that their God was holy and that they were unworthy to stand in His presence. No man could look upon God's face and live.
That this God should enter into the most intimate personal conjunction with a human being, accepting a share in the uncertainties and indignities of human birth, must have seemed initially to be blasphemous. They could have hotly repudiated it unless they had already discovered that God's forgiving grace had come through the human life of the man Jesus, and especially through his death - a mystery even more challenging than that of his birth.
Their account of the virgin birth, therefore, would have been for them anything but a pious legend or a naive wonder story. It was, in a phrase of Paul Tillich, an existential symbol, a sign of the miraculously loving initiative of the holy God in entering right into the heart of a human life. It called attention to a mystery so profound that it could only be apprehended by changing the shape and direction of their whole lives, leading them to what was in effect a new birth in the Spirit.
As such a sign, it may involve theological as well as the obvious biological difficulties. Many thoughtful Christians argue that for Joseph to have had a part in the conception of Jesus would have strengthened rather than weakened the emphasis on the full reality of the Incarnation. But this is not the vital issue. The story stands, as the Early Church came quickly to see, as a solemn testimony that the initiative in the birth of Jesus was not fortuitous but the work of the Holy Spirit who, in the time of this mortal life, enabled God's son, Jesus Christ, to visit us in great humility.
That testimony has credibility for us in the same way as it had for the Gospel's first readers. They already knew the same Spirit as was in Jesus, an actively renewing power, forgiving, reconciling and giving liberating renewal of purpose.
Surely, when even as attractively popular a festival as Christmas can be exploited into insignificance, we do well neither to dismiss nor passively to accept the Evangelists' testimony to the Virgin birth, but to heed it as a pointer to the awesome, ultimate mystery of our humanity, the coming of divinity into our midst in human form.
Dr Daniel Jenkins is a United Reformed Church minister.