From Jesus on a plinth to an angel on Merseyside

Mark Wallinger caused a sensation with his life-sized Christ in Trafalgar Square. This week a retrospective show of his work opens at Tate Liverpool. Simon Grant met him

Mark Wallinger should be very pleased with himself. The 41 year-old artist, shortlisted for the Turner Prize in 1995, will represent Britain at next year's Venice Biennale and this week a "mid-career" retrospective of his work opens at Tate Liverpool. But he is a little more ponderous than you'd expect. "I'm on the way to being venerable, I suppose," he says with chirpy irony. "I reckon mid-career is short hand for middle-aged."

Mark Wallinger should be very pleased with himself. The 41 year-old artist, shortlisted for the Turner Prize in 1995, will represent Britain at next year's Venice Biennale and this week a "mid-career" retrospective of his work opens at Tate Liverpool. But he is a little more ponderous than you'd expect. "I'm on the way to being venerable, I suppose," he says with chirpy irony. "I reckon mid-career is short hand for middle-aged."

Wallinger, who trained at Chelsea School of Art and Goldsmiths, has made a career out questioning how we define ourselves. It is slippery territory, but he loves tackling the big themes. While his earlier work looked at identity through a myriad of subjects - from Royal Ascot, a four screen video showing consecutive years of virtually identical footage of the Queen and Prince Philip waving and doffing hats to the crowds, to A Real Work of Art, a thoroughbred racehorse that he co-owned and that ran the 1994 flat season as a comment on the social politics of sport - he has turned to tackling faith and religion. Could this signal the first murmurs of a mid-life crisis or perhaps a crisis of faith?

"Several years ago it was easier to position yourself," answers Wallinger. "It was easy to say what you weren't for. Now there is a new liberal capitalism it has become much more nebulous. At the moment I am lost in an interesting kind of way, so I am having to make a leap of faith, which is what my recent work is about."

If Wallinger's talk of his work (he's good at avoiding talk about himself) is convoluted and a little rambling, his recent video trilogy - on show at Tate Liverpool - is not. To star in the work he created a character called Blind Faith, an everyman dressed in black trousers, white shirt, black tie and shades. He is a modern blind deity who works as a conduit between past and present. In each video we see him in strange transitory spaces - in an underground station ( Angel), the top of Primrose Hill ( Hymn), sitting in an electric chair ( Prometheus) - reciting mythological and religious texts.

In Angel, he stands on the foot of an escalator, treading towards the camera. He speaks the first five lines of St John's Gospel: "In the beginning was the word and the word was God". It sounds strange. You soon realise that the scene is playing backwards (he had to learn the verses phonetically backwards). The verses are repeated until, accompanied by the triumphant, climactic strains of Handel's Zadok the Priest, he is taken heavenwards, to the top of the escalator. It is a deceptively simple piece of art; ambiguous, humorous, but rich in content.

"I'm dicing with something quite powerful with this character. I'm trying to shape an enquiry that expresses ambivalence about faith," says Wallinger. This feeling is often expressed by looking back at the art of the past and bringing it into the present. "Every era is trying to create its own modernity" he reasons.

Wallinger's video trilogy marked a slight shift from his first, and most public exploration of faith. His sculpture Ecce Homo, the marble resin figure of Christ that occupied the fourth plinth in Trafalgar Square until earlier this year (and, soon, hopefully to be installed outside Guy's Hospital), was highly provocative. In this simple, life-size image, he raised important questions about belief.

"When I was asked to think of a subject, it came to me straight away. I felt that we are now at a point of squeamishness when it comes to faith and I thought we should be thinking about that," he says. For a wavering agnostic, to make an image of Christ is a bold move. It is not a celebratory piece, but acts as a point of enquiry. In a way, it is a self-portrait. Here is Mark Wallinger, standing alone, questioning the whole notion of faith, and asking us to do the same. It was also a powerful political work. Jesus, in his crown of thorns, shorn of hair, works as a metaphor for the story of the political prisoner, be it in the memories of Nazi Germany or the Balkans.

But Ecce Homo was a one-off. Wallinger says he finds sculpture a limiting medium, video is more flexible. It certainly suits the fleeting, open-ended subject matter, best seen in Liverpool in his newest videos Cave (a large-scale work commissioned specially for the exhibition and based on a professional boxing contest) and Threshold to the Kingdom. In this piece a camera focuses on a pair of exit doors at the arrivals hall of London's City Airport. As passengers emerge from the customs clearance, "the nearest equivalent to the confession and absolution necessary before entering the promised land", they pass through the pearly gates, flanked by palm trees, where St Peter, in the guise of a bored security guard sitting at a desk, welcomes them with a blank gaze. Some figures stop and get their bearings, others march forwards towards their final destination. Allegri's Miserere, a setting of the 51st Psalm, is the soundtrack. The work is filled with witty symbolism, a modern rumination on faith, bureaucracy and freedom. Are we citizens, or just passengers in transit to another world? What can we contribute to this one?

A minister that Wallinger met soon after he made Ecce Homo told him that he was a natural theologian. Perhaps his doubting stance makes him a good candidate for the cloth. But being an artist requires a strong faith all of its own. It must be hard to juggle between the two, for as Marcel Duchamp said about art, "as a religion it's not as good as God."

'Mark Wallinger: Credo', Tate Liverpool (0151 702 7400) from 20 October to 23 December