During Lent, those with Christian faith enter a 40-day period of spiritual reflection that recalls Jesus's supposed period of desert reclusion. In our own triumphantly secular society - although sometimes I think this triumph a purely Pyrrhic one - a similar undertaking might be appropriate. Those of us who are without religious faith are, arguably, more in need than the believers of answers to the big questions that - try as we might to divert ourselves - continue to exercise us. Why are we here? What meaning does life have? What constitutes the Good? And what - if anything - will happen to us after we die?

But if we could all do with such a contemplative sojourn, how on earth are we going to find the time - let alone the space? We are increasingly hemmed in by our responsibilities and only the very rich can afford 40 days of desertification - and they tend to take them in the form of adventure holidays crossing the Sahara, with everything laid on, including "authentic" cultural experiences.

I have a proposal: why not spend the next 40 days in a metaphoric rather than a literal desert? It shouldn't be too difficult to contrive - simply remove all aspects of art and culture from your life. That's right, give it up for Lent: all pictures and drawings, music and books, television, film and radio. Eschew newspapers, and magazines; look not upon the glittery face of the worldwide web. Instead, stride out into the world protected only by the flimsy raiment of your own reason, guided solely by the light of your own conscience, and warmed by your own imagination alone.

Belief in belief

In a cultural desert, the mind begins to burrow deep within itself - just as, in an actual desert, a human body seeks shelter among the rocks. Perhaps in this harshly deracinated environment you will be driven to meditate upon the transcendent, a practice that has become dreadfully unfashionable in the present era, lacking as it does the requisite aestheticism.

Of course, it wasn't always thus. Here in Britain, as throughout the Christianised world, religion and art were once inextricably bound together. The churches were direct patrons of the arts, while the wealthy commissioned works the ulterior purpose of which was to effect their own salvation - or, at any rate, indulgence. And then, for the laity, there was art as decorative medium - the interior design of God's house - and art as a votive device: the transactional object by which the faithful drew nearer to His love. Still spookier, there were artworks that partook of the divinity through the fact of their veneration. One thinks of the many statues of patron saints, carried in procession on their feast days, then called upon
to prognosticate, heal the sick and work other such miracles.

As it was with the visual arts, so it was with literature and music; in the past, the belief in God may not have been omnipresent, but the belief in the belief in God certainly was. Right up until the 19th century, even the most daring and provocative dissenters continued to cloak their artistic productions in off-the-peg theism. Just as I remember, as a boy, reading Victorian novels and wondering whether or not any of the characters had sex - because there was no mention of it whatsoever although they still managed to procreate - so, as a philosophy student, I was perplexed by David Hume's blasé references to his creator even though every aspect of his scepticism disallowed any such faith.

I would argue that it was neither the Enlightenment nor the mechanised march of science and technology that finally put paid to this unquestioned belief in belief, but the man-made cataclysm of the First World War. If I were to choose a suitably iconic image of the impact of the war on faith, it would be the statue of the Madonna that stood atop the newly completed basilica in the town of Albert, immediately behind the British trenches of the Somme. Early in the war, shelling tipped this statue to the horizontal, so that it looked as if Mary was about to throw away the infant Jesus cradled in her arms. The satiric import of this was not lost on the British troops, who henceforth referred to the statue as "the Lady of the Limp".

As Paul Fussell - the historian to whose masterful work The Great War and Modern Memory I owe this vignette - so perceptively argued, after the carnage of the First World War, irony came to be the dominant form of modern sensibility and understanding. Against such devastating facetiousness, what chance had the Lady of the Limp?

It may surprise you to learn that I often visit churches - and not merely to regard them aesthetically, but also so that I can lose myself in spiritual contemplation. It may not be prayer as it is commonly understood by the great mono­theisms, but I find that by setting my own fears, hopes and concerns against the great span of the universe, their trivial scale is exposed. I choose churches because they are purpose-built for such exercises; it is difficult to keep your thoughts base and petty when you are confronted by the vertiginous upthrust of English Perpendicular. True, I like my churches to be old, or large, or both - I'm less likely to step into my local place of worship, because, in common with so many others, the great whirlwind of irony has sucked all the beauty out of it.

Holy watercolour

Since the First World War, then, and with still greater velocity after the Second, art has quit the temple precincts. We can picture this as if it were a frieze, seeing in profile all those painters, architects, musicians and poets bowed down under the instruments of their mysteries and heading for the exit.

Modern churches have lost their patrons and their punters; with a few exceptions, their interiors are bereft of the rich ornamentation of the past, and as for their architecture, well, if we thought the neo-Gothic was bad enough, what can we say of the warehouses of the Lord that have been thrown up in the postwar period? Such decoration as is commissioned for these churches tends to be the visual analogue of the Good News Bible - all primary colours, woody tones and paschal lambs that bear a family resemblance to the Teletubbies.

As it is with ecclesiastical visual arts and architecture, so it is with the wider cultural ambit. Yes, there are still men and women who write godly verse and score sacred music, but the real fixed point to which transcendent belief is tethered is the ironic stake modernity has driven through the heart of faith. A couple of years ago, I found myself in the locked vault of a jeweller's in Hatton Garden, in central London. I was there, together with the artist Damien Hirst and a couple of other hangers-on, to handle his piece For the Love of God, a human skull transmogrified into a colossal bauble that comprised a sheet of artfully shaped platinum embedded with hundreds of diamonds.

On the cusp of the financial meltdown, Hirst's skull was being valued at £20m; he told me he had named it thus because "For the love of God!" was what his mother had exclaimed when he told her about the piece. Two things struck me: first, the extreme ironisation of faith embodied in the diamond skull, and second, the effect it had on my companions when they held it. It was as if they had taken a lungful of nitrous oxide and were transported into a state of giggly and shameless devotion to Mammon.

For the Love of God crystallised my thinking about Hirst and contemporary art. He is, I think, a more primitive figure than we have come to expect artists to be; rather than merely representing the world, Hirst is a shaman who invests objects with a symbolic power that - under the right conditions - becomes real. Mostly this is the power of money itself - but he also employs the powers of celebrity, sex, death and intoxication. We shouldn't be too critical of the highest-earning living artist, because he got that way by perfectly exemplifying the sacred rituals that underpin the true religion of Britain today, aesthetic humanism.

During this Lenten period, few Britons will repair either to the desert or to the deserted churches, but they will descend in droves on the temples of arts and culture, many of which are handsome, beautifully maintained buildings chock-full of valuable votive artworks.

In the past 20 years, as church congregations have continued to dwindle, the art galleries and museums have increased their visitor numbers hugely. Exactly like the religion it has replaced, aesthetic humanism demands of its followers certain rituals - silence, rapt concentration, a catechism in the form of a catalogue; and certain beliefs - the holiness of the artistic vocation, the intelligibility of taste (its equivalent of divine grace), and the temporal authority of those curators, dealers and arts administrators who are its priesthood.

Shorn of any faith in God, the arts have become imbued with the qualities of a secularised religion. The only immortality anyone believes in now is the immortality of the artist, whose soul is encapsulated in his works for all eternity. The modern Medicis have great faith in the arts - they enrich themselves by speculating in scraps of canvas and lumps of metal, and by endowing the public temples, they too hope for immortality.

As for the laity, whether we reverence an index of approved works, or indulge in that liberty of conscience summed up in the credo "I-don't-know-much-about-art-but-I-know-what-I-like", the important thing is that we believe: we believe in the superiority of man-made beauty over any other aspect of the natural world, and in the capacity of art to express all our thoughts and feelings. Our artistic faith also provides us with emotional succour and psychic balm. When we have retired, we go on pilgrimages to the Guggenheim in Bilbao, say, hoping to imbibe as much holy watercolour as we can before we are anointed with oil paint and die.

Like the Christianity it has usurped, aesthetic humanism has a Trinity - albeit one in which paternity is inverted, for it is Man who is now the father, and the old Roman goddess Fortuna whom we have made in our image, as our hidden hands manipulate the market in artefacts into being. As for the Holy Ghost, what could be more immanent (and yet transcendent) than the internet, which is everywhere and nowhere at once, transmitting our divine creative spark?

Art atheism

As I have proposed the existence of a new religion of aesthetic humanism, it is reasonable to ask whether I myself am a communicant. But I suspect you know the answer already: I may lack traditional religious faith, but I find myself an even more strident recusant - a heretic, even - when it comes to the arty church. It is an unpalatable fact, like an extra-dry communion wafer, that economic downturns can be good for the arts. During the last recession, the "Young British Artists" emerged as a phenomenon that at first satirised faltering capitalism, and then capital­ised on its resurgence. It might have been hoped that this recession would be deep enough to inaugurate a complete re-evaluation of the aesthetic humanist credo; that there might be a reformation to rival that of Christianity in the 16th century.

Sadly, or perhaps thankfully, it doesn't look as if this will be the case. Our deep faith in Fortuna's free market remains intact, and no dissident theses have been nailed to the doors of Tate Modern. Archbishop Serota sits secure on his throne. As for me, I find I do need a period of contemplation away from the hurly-burly of religious gallery observance. I feel strangely drawn to visit a modern church, where it's quiet and calm, and divinely ugly.

Will Self launches a series of six talks for Lent on Radio 4, 24 February (8.45pm)