Things ain't what they used to be. Ten thousand people are expected to converge on the Royal Highland Showground in Ingliston at the weekend for an event which is modelled on Scotland's big indie music festival, T in the Park. It is organised and sponsored not by impresarios and a brewery but by the Church of Scotland. T and Scones in the Park?

The Saturday/Sunday festival will be a mix of music, dance, art and "food for thought". The showground will become a tented village in which many local churches will show off their wares and share their stories. As part of the whole event, a youth festival will be held in a huge shed at the Royal Highland Centre. It will feature bands, speakers, street art, urban dance, big-screen DVD's, X Factor competitions, basketball, DJ concerts, beauty therapy, chocolate fountains and chill-out areas. Chocolate fountains and Presbyterianism?

Although organised by the Kirk, the festival will be ecumenical in nature, and speakers will include Cardinal Keith O'Brien and the controversial Anglican Archbishop of York, Dr John Sentamu. There will be innovative and lively worship. The Richard Dawkins challenge will be addressed by two theologians who have written books on the subject, Alister McGrath and David Robertson. Organisations such as Tearfund will be available to talk to young people to encourage their involvement in voluntary and gap-year opportunities in Scotland and all over the world. Groups such as Christian Aid will encourage people to buy fairly-traded goods.

So what's this big jamboree all about? Here's the background. Recognising the decline of religious observance in Scotland over several decades, the Kirk set up a group called Church Without Walls. Part of its remit was to find new ways of expressing Christian faith in a post-modern cultural context which is at best indifferent and at worst hostile to religion. Over the past 50 years or so, big institutions like the trade unions and the mainstream Protestant and Catholic churches have fared badly, both in terms of numbers joining and the erosion of public authority. The old Kirk conveyer belt which carried young people from baptism to Sunday school, to youth fellowship, to confirmation, to church marriage, to baptism for their children, ground to a halt a while back. Catholic and Protestant churches are often perceived as hating a new world they don't understand.

In this crisis, there have been two extreme temptations. One is to turn up the volume, hoping that people will repent and that the "good old days" will return; the other is to wring hands and capitulate to the spirit of the age, echoing the words of Groucho Marx: "God is dead, man is dead, and I'm not feeling too well myself."

The Church Without Walls people have rejected these two options. They have argued persuasively that the good old days weren't so good, and that the post-modern phase provides an opportunity for the churches to reform themselves around the core Christian message and express the faith in new and imaginative ways. One of the leading movers, Rev Albert Bogle, says: "It seems to me there is a holy discontent within the nation, people today are looking for more - but not just in monetary terms. They are looking for purpose, for inspiration and, above all, to reconnect with a faith that is relevant for everyday life."

It's increasingly evident that the consumer culture can deliver geegaws but not happiness, material goods but not meaning. Individualism without community is seen to be empty. Does that mean that thoughtful people will flock back into the old churches? Certainly not to churches which hector people, marginalise women and stick the boot into gays, or which imagine they have a divine right to be deferred to by the state and heard by the nation.

What the mainline churches do have to offer is two millennia of spiritual riches. Their job is to keep alive the rumour of God, and share out what treasures they have. If they are serious about this, the churches need to find a new and richer vocabulary, a more life-enhancing grammar. Since returning to the rough old trade of journalism seven years ago, I've been struck by how much the churches have been used to talking to themselves in their own rather tired jargon.

I wish this national gathering well. What John Knox would have made of beauty therapy and chocolate fountains, I can only guess. I'm all for "holy discontent" in post-modern Scotland, and opportunities for new dialogues with the fathers and mothers of the faith. The time for hand-wringing is over, and the auld Kirk is trying to sing an imaginative new song in a strange land, a land in which the cultural tectonic plates have shifted and things will never be the same again.