Late last month in his hometown of Salem, Oregon, Larry Norman gave his last U.S. concert.

Most people do not know who Mr. Norman is. But more and more Americans are becoming familiar with his legacy. The 58-year-old singer is widely considered to be the "father of Christian Rock." He was the first person to achieve commercial success by combining Christian lyrics with rock and roll music. And while Larry Norman may be retiring, the musical genre he helped to create back in 1966 continues to rock on. Just ask the 80,0000 people who have gathered on a warm summer evening in Central Pennsylvania for a concert.

Set in a natural amphitheater, surrounded by lush, green mountains, the annual concert is a 4-day affair. This year, the opening act is a band called '," she sings. It is a light, upbeat, almost bubbly mantra that the audience responds to in kind.

With their fresh faces and modest dress, Becca, Alyssa, and Lauren Barlow seem pretty tame. But do not be fooled by their appearance. As the sweet mantra quickly changes to a drum and electric-guitar-laden ballad, it becomes clear that these girls know how to rock.

BarlowGirl released their 1st album last year. It has sold more than 250,000 copies -- not bad for any band, but when you consider that the 3 Barlow sisters have a somewhat unorthodox message, the group's record sales are especially striking. Between sets, Lauren Barlow announces to the crowd that God does not want the teenagers who attend her concerts to date. At all.

"So we're all mad, we're like, 'Why don't you want us to date, God? What's the deal with that?'" she recalls, telling her audience that she and her sisters we not at all pleased with the answer they got when they prayed to God and asked for guidance on the topic of dating. But then she relays the rationale that she and her sisters say God gave them. "He's like, 'Because I have not created my children's hearts to be broken.'" The crowd cheers wildly. Lauren Barlow's unorthodox message has resonated with them.

BarlowGirl is one of the latest additions to the Christian rock music industry. More broadly referred to as "Contemporary Christian Music," the industry posted more than $700 million in sales last year. That is more than the jazz, classical, Latin, and soundtrack industries combined. The music itself is not all that different from what you might hear on a Top-40 radio station in the United States. But the lyrics -- and the lifestyles led by these musicians -- set Christian rock bands apart.

Instead of singing about drugs or sex or violence, Christian bands often refer to "God" or "the Creator" or "Jesus" in their songs. Brian Newell,30, says that is why he listens. "When I was not in my life with Christ, I used to love [the secular band] 'Nine Inch Nails,'" he says. "They knew all my problems. The only difference was they didn't have any solution." He laughs. "They weren't telling you that there was hope. They weren't telling you that there was a way to persevere, a way to go forward."

To be fair, not everything you hear in the secular rock industry is about drugs and sex. In fact, these days, you will often hear songs that are quite inspiring on mainstream radio stations -- songs that are about family and love and finding meaning in one's life, such as "Meant to Live," which spent 14 weeks in the Billboard Top 10 last year.

The song tells listeners who are caught up in the trappings of popular culture that life is about more than what is found on television or in magazines. It was released by the band -- which, interestingly enough, began its career as a Christian rock band. It is one of a handful of groups that have crossed over into the mainstream in recent years, and according to Dave Douglas, drummer for the Christian band Relient K, Americans will probably be seeing a lot more of this. "I think that the line between what is considered Christian vs. secular is kind of becoming more and more blurred as time goes on," he says. "One or two labels kind of took a chance on a band that they thought could have success in a mainstream market, and it worked, so I think more people are taking a chance on it. I don't know if it's necessarily anything that's different with the music."

Not everyone agrees with Dave Douglas on that last point. Switchfoot may be a Christian band -- and it may still play Christian rock festivals like this one in Pennsylvania -- but "Meant to Live" does not mention God or Jesus anywhere in the lyrics. It does mention "Providence," but for some Christian rock fans, that is not enough. Indeed, the industry has a term, "J-P-M," which stands for "Jesuses Per Minute" and describes the reality that if a song does not mention God enough, it will not be played on some Christian rock stations.

Still, the Christian ministry does not have to involve proselytizing, according to John DiBiase, who runs the Christian music website, "Even if people will pick up a band like Switchfoot and not necessarily find, you know, a blatant 'Jesus Loves You' message in it, there's still hope in it," he says. "There's still a lot more positive stuff. They're not people celebrating drugs and alcohol and pre-marital sex and stuff like that. There is a higher importance [placed] on morality in Christian music, and I think people want that."

And if bands like Switchfoot? or BarlowGirl? or Relient K can somehow have an influence on the secular rock industry - and get mainstream artists to tone down some of the negative imagery that is prevalent in their music - then John DiBiase says Christian rock bands will have served their God well.