Music critics have tended to shun Christian rock, believing that the devil has the best tunes. But the genre is becoming hugely popular in Ireland and elsewhere.

Tomorrow's World Youth Day Mass in Sydney, Australia, is expected to show that God can still draw bigger crowds than U2 and the Rolling Stones. Up to half a million people, including young Irish pilgrims, will attend a Mass celebrated by Pope Benedict.

The event has been dubbed "Woodstock for Catholics''. As one papal theologian noted this week: "There is usually a lot of sleeping on the ground while listening to music, making friends and even falling in love.''

Christian leaders may wring their hands at falling church attendances, but they could see an exciting opportunity in the soaring popularity of Christian music and spiritual gigs aimed at young people.

The first ever Making A Difference (MAD) Christian rock music festival at Ballinacoola, Co Wicklow, last month was a surprise hit. Although there was little media hype surrounding the spiritual pop festival, 1,600 people turned up to see acts such as One Hundred Hours and Elation Ministries strut their funky stuff on stage.

Even the organisers seemed quite taken aback by the popularity of the festival.

"It was put together at relatively short notice, but there was a huge reaction," said one of organisers, Stuart Kenny, a leading light in St Vincent de Paul. "Originally, someone came up with the idea of having an event to welcome young people to the area and it just grew from there.

"I think there was a real desire among young Christians to have an event such as this."

The event now looks set to become God's answer to the Electric Picnic.

The most popular Christian event for young people is Summer Madness in Belfast, which is held in early July. Originally devised by the Church of Ireland youth department, it attracts 5,000 people each year.

The season of gospel grooves will continue next week when another large crowd of young people gathers in Mayo for the Knock Summer Youth Festival.

The pilgrims will sleep on air mattresses in large marquees at the retreat, which will last from Thursday to Sunday. Participants will pay €55 for the four days, with food, accommodation and transport included. By comparison with events such as Oxegen, it is considered a bargain. When the Catholic youth event started in 2002 the crowds were small, but it has grown steadily in popularity and more than 1,000 are expected at next week's retreat.

"I think these events are growing in popularity among young people because they can have a very powerful experience,'' says organiser Anne Lee. "It is very social, except the focus is not on getting smashed. We are meeting young people's deeper desires and needs.''

While the Knock festival is Catholic, MAD is more evangelical in tone. There is some overlap between MAD and the Knock event. Elation Ministries appeared at MAD and are also on the Knock bill.

Ronan Johnston, the composer and former You're a Star musical director, is also involved with both festivals.

The growing popularity of spiritual rock, or Contemporary Christian Music (CCM), is part of an international trend, according to Stuart Kenny.

"Christian music is now the fastest-growing sector in the world. It is a 21st-century phenomenon.''

While total music sales have dropped over the past five years, Christian music sales have increased steadily. The Observer recently reported that the genre now sells more than classical and jazz music combined.

Record companies such as EMI, Sony and BMG have launched their own religious labels or bought shares in Christian record companies.

"The bands deal with many of the same issues and desires as ordinary rock music, but they do it from a Christian point of view,'' says Stuart Kenny. "They are looking for an alternative to the nihilistic view of life that you see in a lot of rock music.

"There is no alcohol and no drugs at our event. These people don't need drugs.''

Instead of booze, revellers at MAD make do with smoothies, coffee, ice cream and the power of prayer.

There is nothing new in Christian rock, of course. Some would argue that rock is simply going back to its roots in gospel music. The evangelical Jesus Movement has inspired bands since the 1960s.

Attempts by Christians to look trendy and keep up with the times have frequently been the subject of ridicule. Who can forget Graham Norton's star turn in Father Ted when he played the nauseating, folksy priest, Noel Furlong, singing in a caravan?

Ronan Johnston believes Christian music will never escape this worthy image.

"We have to face the fact that the gospel message is not very cool. But it is challenging and can be very powerful.

"I think Christian music works best if it is not banging people over the head with its message. It should not be just a cheap, knock-off of rock music, either.''

Any attempt to bring this Christian rock into conventional churches is likely to be met with stiff resistance from traditionalists, who regard it as happy-clappy claptrap.

Some conservative Christians feel that the medium of popular music is, by its very nature, unholy and so unworthy of inclusion in a religious service.

The Christian philosopher Roger Scruton has argued that rock music arrests people in a state of adolescent psychological immaturity.

Although Pope Benedict presides over Catholic World Youth Day, he has been critical of rock music in the past.

Before he became pope, Benedict said rock had no place in the liturgy and that rock concerts were pseudo-liturgies that lifted people out of themselves with a counterfeit mystical experience.

Now that he is pope, however, he is unlikely to turn his nose up at such a vast crowd of young people yearning for spiritual fulfilment.

- Kim Bielenberg