In the premodern worldview within which the Christian tradition was fashioned – and which still prevails in the minds of many people – a supernatural reality was thought to be essential. It was central to religious experience, gave people a sense of worth and identity in the wider scheme of things, explained much that was baffling in the world around them, and offered certainty beyond this life.

In society at large today that sense is withering away. The metaphysical speculation on which it feeds no longer carries wide conviction. Some will regret that but others will see it as opening new ways of understanding faith that belong more naturally with the fruits, not only of the huge advances in human knowledge over the past four centuries, but also of modern theological exploration.

That raises the question: Can there truly be mystery and transcendence without a sense of the supernatural impinging directly on human life and destiny? Indeed there can – provided we are open to a radically new approach that continues to uphold mystery and transcendence as central to religious experience but does so in a quite different way.

For dispensing with the supernatural does not rule out mystery. Now though, it is not so much the mystery of the ultimately unknowable but of human life itself. Awe and wonder may be a better way of expressing that if only because those who focus on mystery sometimes brandish it as if it were a supernatural trump card. “Ah yes,” they say when logical argument runs out, “but beyond all that is elusive / ineffable / ungraspable / indescribable / inexpressible / intangible (take your pick) mystery.”

Mystery then becomes an unchallengeable hidey-hole in which ‘the God of the gaps’ can repose for ever, (‘the God of the gaps’ being the explanation for everything that cannot yet be explained by science or other knowledge).

So where does religion sit in relation to mystery today? Here Christianity rethought from a secular perspective has much to offer, stemming from the dual vantage point that it is both the most secular of the world’s great faiths and it is within the Christian West that secular culture has taken root.

There are good reasons for that, beginning with the church’s most innovative doctrine: the other-worldly God of old became human flesh and blood in Jesus of Nazareth. God was earthed. The human (and not just the human Jesus) became the locus of the divine. This insight is so astounding that it is only slowly being rediscovered, after lying dormant for 2000 years.

Sir Lloyd Geering points out that this revolutionary perspective proved too much for the early church which took the opposite tack: instead of teasing out the implications of making God human, it poured its creativity into making Jesus divine. Drawing on the cosmology of the times, it imagined Jesus as having been sent by God from a heaven that was as real as Earth, to be born in Palestine; and after his death and resurrection it returned him bodily there. In heaven, say the church’s 4th-century creeds, he reigns over creation as a full and equal partner with God the Father and the Holy Spirit, three aspects of the one Godhead.

It was inevitable that mystery gathered around Jesus in that heavenly world, and for hundreds of years theologians wove their interpretations around that understanding of God in his heaven with Christ at his right hand and humans sweating it out on Earth.

A secular Christian faith, by contrast, grows naturally out of affirming that incarnation or enfleshment of God in human form. It does not locate a supernatural God in a faraway heaven, nor insist that Jesus is “divine” in the traditional sense. Instead, it interprets Jesus as a man whose life makes total sense within this world of space and time.

That affirmation of humanity as the locus of the divine does not mean abandoning any notion of mystery and transcendence. It simply reinterprets them so that they belong naturally within our secular experience of the amazing miracle of life.

Transcendence climbs across (that is what “transcendent” means) the confines of our everyday existence to give a glimpse – and an experience – of a quality of life that excites, transforms, enlarges, satisfies and renews. The divine becomes incarnate.

That is mystery. And that mystery is what Christmas is all about.