SOME artists in the Christian tradition have tried to imagine a biblical scene as it was in Palestine some 2000 years ago. Roger Wagner is not an archaeological painter in that sense, trying to recreate the past. His paintings are a response to the modern world, but he tries to show the world we live in now, "burgeoning with a biblical element", as he puts it. How does he do this?

In this picture, our eyes are drawn first to the old Battersea Power Station and the cranes looming over the wharf, all meticulously painted. In some ways, Wagner is a very traditional painter, showing every detail with great care and skill, as can be seen, for example, in his superb studies of trees on Port Meadow in Oxford. So it is not surprising that a big work of his can take a year.

Then we notice two tiny figures on the Thames, and the title, Walking on Water III, gives us a clue about their identity. Based on the incident in Matthew 14, we see Peter, the figure on the left with his left arm reaching out, trying to walk on water, and then becoming terrified, as he feels himself sinking. Christ, on the right, holds out both welcoming arms.

One of the features of Wagner's paintings is that the main figures are often barely noticeable against the wider urban scene or landscape. In the world's terms, the Christian faith is a hidden affair, and the deeper story of God at work seems marginal against the great power struggles of men and nations, perhaps epitomised here by the vast power station.

Yet it is this deeper story that matters - and perhaps it is, above all, the intense blue light that brings out the ultimate, transcendent significance of what is going on. The light gives an unearthly, surreal effect; what is happening is in time, but not our time.

Light plays a crucial part in Wagner's paintings, at once illuminating and probing, showing things as they are and as theymight be, and indicating that something more is going on than can be seen by the naked eye.

Wagner says that, when visiting Venice when he was 16, and going to an exhibition of surrealist painting, he was bowled over by The Rose Tower by Giorgio de Chirico. It seemed to suggest something strange going on. He could see the poetry in the painting. Wagner himself has retained this capacity to indicate this something more: something the eye sees, and does not see.

In the light of that extraordinary light, even the tiny details in the picture seem to take on a new significance: the arms of the crane like a cross, its weighted buckets, all beautifully balanced; the world held in equipoise; the gulls flying with joyous liberation; and the Thames itself with a deep, shining stillness.

Many other painters have set biblical stories in their own times, against Tuscan landscapes and royal courts, using figures in contemporary dress. But Wagner does not just want to recreate a biblical scene in 21st-century clothing. He wants to indicate another dimension altogether. He is also an accomplished translator and poet, and perhaps the best commentary on this painting is his sonnet.

To step out of ourselves on to that sea
Forsaking every safety that we know
Becoming for one moment wholly free
That in that moment endless trust may grow.
To step into that love which calls us out
From all evasions of one central choice
Besieged by winds of fear and waves of doubt
Yet summoned by that everlasting voice.
To walk on water in astonished joy
Towards those outstretched arms which draw us near,
Then caught by winds which threaten to destroy
We sink into the waters of our fear.
Yet underneath all fears and false alarms
Are sinking, held, by everlasting arms.

So, in the end, this painting evokes our life of faith now. It brings to mind the wonderful poem by Francis Thompson, in which the poet cries out in his destitution, "clinging Heaven by the hems; And lo, Christ walking on the water, Not of Gennesareth, but Thames!" ("The Kingdom of God").

From one point of view, Wagner's paintings seem startlingly literalist in their approach,as in the remarkable The Harvest is the Endof the World and the Angels are Reapers,which shows large angels reaping the wheat. It is not, you would have thought, the most obvious scene to appeal to the modern mind, but it is totally arresting and unforgettable in its effect.

Here, in Walking on Water III, the scene is in one way also very figurative and physical, depicting two figures actually walking on the water of the Thames: but this Thames is all that threatens to overwhelm us. It is our world, but our world lived in the light of faith.

The Rt Revd Lord Harries of Pentregarth is the former Bishop of Oxford, and the author of The Image of Christ in Modern Art (Ashgate, £19.99 (CT Bookshop £18); 978-1-4094-6382-5) (Books, 20 December). This Lent series is based on the book.