Each generation adds a few new festive traditions - and in our own times one essential seems to be a cleric popping up to deny some central aspect of the Christmas story.

Right on cue, we have Giles Fraser telling us that the Virgin Birth "goes against the grain of Christianity". An intriguing claim, you might think, given that we usually work out what the "grain of Christianity" is by consulting the Gospels and the Creeds, rather than the opinion pages of the Guardian.

That gets us to the heart of what is wrong with Giles' argument. He relies on the truth of the Creeds and Gospels to get going. Without believing they are inspired by the Holy Spirit, none of us would have grounds to believe in the incarnation in the first place!

Yet, when it comes to the doctrine of the Virgin Birth, the stories we read in the Gospels and the proclamation of the Virgin birth that Christians have recited for generation upon generation seem to be given no weight at all.

At the heart of the Christmas message is something the modern liberal mind resists: the idea of a revelation, of something we as humans could not have worked out on our own. Human reason alone might have taught us that God needed to be worshipped - even, perhaps, to be placated because of our selfishness and faithlessness. But reason alone would never have taken us to find him in a manger or upon a cross. Only God's self-revelation can teach us that.

None of this is to suggest that revelation and reason are somehow competitors. Far from it: it is because there is a good and loving God that our reason can be trusted. Justin Martyr (c100-160 AD), rightly held Christianity to be the true fulfillment of all philosophy, because the human capacity for reasoning is in fact a reflection of the divine reason (logos) which has become flesh in Jesus Christ. That is why, as Nick Spencer and I have argued, Christianity provides the firmest foundations for human reason and for humanistic values.

So Christmas is a feast for philosophers, for sages from the East (or West) as well as for shepherds. But it reminds us that true wisdom is found first by kneeling and adoring - by listening to what the Holy Spirit has revealed to us in the testimony of Scripture and the Church.

So, happy Christmas worshipping the God who was incarnate of the Virgin Mary and was made man!

Canon Dr Angus Ritchie is executive director of the Centre for Theology and Community.