Taking the stage amid whistles and shouts, Jars of Clay prepares to turn Chicago's House of Blues into a rowdy house of worship.

Every booth, barstool and nook circling the basement stage is packed for the free "After Five Live" concert. As keyboardist Charlie Lowell sounds the evening's opening chords on electric piano, singer Dan Haseltine pleads in a heavenly direction, "I need you, I need you, I need you/You're all I'm living for."

Jars of Clay's lyrics reflect a Christian view — a nuance that may be lost on many in the club crowd, especially when the "you" could easily be, say, a lover. But since scoring its first hit, "Flood" in 1996, the group has made little secret of its Christian orientation.

Six years ago, Jars of Clay was one of few Christian acts bold enough to play outside churches and religious festivals. But today, the band is hardly alone in taking a Christ-inspired message and music to the masses — and instead of balking, the masses appear to be embracing. Witness the success of P.O.D., Lifehouse, Sixpence None The Richer and Creed.

A separate class of bands that "preaches to the choir" — that is, plays to Christian audiences — also looks to be gaining ground. While the rest of the music business is reeling from slumping record sales and piracy fears, sales in Christian music grew in 2001 — though gauging the size of that growth provokes heated debate among industry insiders.

But that growth and increased visibility has created tension — and an identity crisis.

So questions arise: What is Christian music and whose music is it anyway?

Right now, contemporary Christian music — which includes rock, pop, gospel and R&B styles — is at a crossroads. Some believe it should be what it has always been, music made by Christians, largely for Christians, to encourage Christians.

Others counter that entertainers need to heed Christ's call to go out into the world and preach the gospel — and that as such, they need the encouragement and resources to compete with the Madonnas and Matchbox 20s of the world.

One thing that is not disputed: Music by Christians is growing in sales, exposure and marketing might.

Gospel and contemporary Christian music titles sold just shy of 50 million units in 2001, which represents a 13.5 percent jump from 2000, according to the Christian Music Trade Association in Nashville. But those figures are suspect because they include albums such as the "O Brother, Where Art Thou?" soundtrack and Mannheim Steamroller's "Christmas Extraordinaire."

"I hope it's not so they (Christian record labels) can show (inflated) growth to their mainstream owners," said Mark Joseph, author of "The Rock & Roll Rebellion: Why People of Faith Abandoned Rock Music and Why They're Coming Back." He argues that only a chunk of "O Brother" sales should count as "Christian music," because most were not made in Christian bookstores.

"The (CMTA) numbers are not accurate, although what they are saying is true — there is growth," said Chaz Corzine, part of the management team that handles Michael W. Smith and Amy Grant. "What we ought to tout is that there really is significant growth, especially when you compare Christian music to other genres."

Blame the cloudy figures partly on Billboard and SoundScan. Because the trade magazine and record sales tracking group count "O Brother" in multiple formats — in this case, country and Christian — it tends to inflate sales figures in the Christian market, said CMTA president Frank Breeden.

"We make no bones that this is not a core album from one of the artists in our industry," Breeden acknowledged. "Very wisely, we look at 'O Brother' as a wide elephant in the room — and even without it, sales are still up 9 percent."

As for what's fueling a Christian music boom, observers point to several key reasons. First is a reaction to Sept. 11. Christian music was rising in popularity before the tragedy, and only a temporary spike in sales came after the terrorist attacks.

Still, many believe that something in that event stirred a deeper need for music perceived as healing and hopeful.

"In the post-Sept. 11 community, we're looking for something comforting — something to bring us back to the security and faith of our parents — and I think Christian music is helping to do that," said April Hefner, former editor of CCM magazine, a publication that follows the contemporary Christian music world.

The genre is also in a much better position to market itself than it was a decade ago. Today, most Christian labels are owned wholly or in part by major labels — meaning that they have clout to spare.

"There's been more interest from (major label) parent companies and companies that have the mojo to get the word out there," said Christian pop star Smith, who owns Rocketown Records. "In the 1980s, they wouldn't give us the time of day."

A third factor is that not much innovation is going on in music as a whole. The preponderance of boy bands, bland blonds and potty-mouthed rappers has left listeners willing to give Christian artists a shot.

With all that growth, aspiring talent can more easily break into the music business via the Christian industry than other channels. But musicians of faith debate whether to align themselves with the Christian music industry proper or strike out on their own.

More than at any time in its history, Christian music is developing along two distinct lines: a traditional "music ministry" path where artists record songs for the church and other Christians, and "message music," where a Christian point of view comes through in content that might address any subject. Perhaps the best example of the latter is U2, which began its career playing church shows but would not be considered a "Christian rock" group.

Why the distinction? Much of that has to do with the Nashville-based Christian music industry. Besides being the home of country music, Nashville houses a host of Christian record labels — many of them owned by major-label parents — that sign artists marketed primarily via Christian bookstores, record stores and Christian music festivals such as Cornerstone (held each July in Downstate Bushnell).

In Nashville, artists have studios, musicians, management, booking agents — even pastors who go on tour with bands — at their disposal. But the records that come from this system often have a stiff, same-sounding quality.

Spiritually as well, there can be a stultifying sameness. While Catholic and liberal-leaning Christians can be found making fine music, they are the exception rather than the rule in this bastion of conservative Christianity, dubbed by some players as the buckle of the Bible belt.

Artists pay a price in exchange for making a life in Christian music. For starters, Christian radio stations and bookstores keep close tabs on song content. There is an industry slang term in Nashville known as "JPMs," or "Jesuses Per Minute." This unwritten rule states that if a song doesn't mention Jesus or God enough in its lyrics, it fails to get airplay or the proper push from a record label.

"I've heard stations say, 'We can't play this, the words are way too intelligent and our listeners are used to mediocre music that's easy to digest,' " said Ginny Owens, who is signed to Rocketown. "But then again, that's no different than top 40."

Any form of cursing, even mild, can get an act in hot water.

"It has been a fearful industry in that there's not a lot of artistic license," said Ashley Cleveland, a two-time Grammy winner for Best Rock Gospel Album. "I don't fit in naturally anywhere because I'm a little bit of an offense to the Christian industry and too Christian for the mainstream. But the beauty of that is I have a lot of artistic freedom and I can function in situations that not many Christian artists can play in."

One of Cleveland's biggest complaints about Christian music is that it apes the mainstream — that is, whenever an act such as Weezer becomes big, Nashville labels rush to find and sign "the Christian Weezer." "If you embrace the truth of the gospel and embrace your gifts to the fullest, then we should be leaders," Cleveland said. "And so much of Christian music is imitative — it's formulaic and you have Christian versions of popular artists. That in and of itself is very uncool."

Blame such creative clumsiness on growing pains. "It's in its adolescence, it's a fairly young industry," Corzine said.

Grant was among the first pop gospel performers to taste mainstream success with her No. 1 Billboard pop chart hit "Baby Baby" in 1991. Some trace the origins back further, to the late 1960s and the "Jesus People" movement. Around that time, many Bible Belt Christians considered rock "the devil's music." Then came "Good News," a 1967 folk-rock musical written by a trio that included Billy Ray Hearn, who went on to be a Christian record company executive. "Good News" sold 300,000 copies and opened the door for experimentation among Christian artists.

Today, platinum-selling bands that have braved the mainstream such as Jars of Clay and P.O.D. have learned to walk a fine line between luring Christian and non-Christian fans. "When you first look at P.O.D., they're not wearing minister's garb," Itzkoff said. "They seem to be what a heavy metal band would be. And with their last couple of singles, it (the content) wasn't so explicit, though certainly if you broke it down you could decode it."

Being subtle, he stressed, is key. "As a listener," he noted, "you don't want to be hit over the head so hard."

"For us, there's a gravitational pull toward being a stereotypical Christian band, so you either try to get out of that box or let it swallow you up," said Jars guitarist Matt Odmark. "It requires a sustained amount of intention to look for new ways to present ourselves."

Still, P.O.D. has had to make minor concessions. It changed the cover art for its album "The Fundamental Elements of Southtown" to remove items such as a cigar at the request of Christian retailers, who branded the jacket as "pagan."

Then there are those artists who have fled the mainstream for the pop gospel world.

In 1993, The Katinas signed an eight-album deal with Arista Records, based on a performance of their Christian songs for label head Clive Davis.

But shortly after signing the contract, the group was given material that made it squirm, typical R&B fare such as "Sleeping With An Angel" — a song about getting a girl in bed.

After two weeks of fasting and prayer, the group was released from its deal — "a God thing," member John Katina calls it — and now he and his brothers record for Gotee Records.

"We just want God to open the door; we don't want to manipulate the system," Katina said. "We're just not going to drop everything and say, 'Hey, let's go for the general market."'

Indeed, some in the business have a vision that one day Christian labels will transform themselves into a "farm system" for the major labels. Any act that can sell 250,000 copies in Christian bookstores could move up and get a shot to share the bill with a hard-rock band like Korn (This is not as far-fetched as it sounds; P.O.D. has performed with Korn.) Another possibility is that rockers and songwriters of faith will make like P.O.D. and sidestep the Christian industry altogether to avoid any potential fan backlash. "P.O.D. allow(s) themselves to be characterized as a rock band, not a Christian rock band, but they are very open about their faith," Joseph said.

"That's a winning model as we transition from the old era into the new era."

Those artists who prefer calling Nashville home may not have the same reach via MTV or commercial radio.

But as Smith noted, "There's no doubt the music has definitely gotten better, which is awesome. We didn't have the bar raised high enough, but that's different today. We're rocking."