ATLANTA — When brothers Alex and Stephen Kendrick were looking for inspiration for their third feature-length film, they turned to God for help.

"To be honest, I prayed about it," Alex Kendrick said. "I said, 'God, would you give me an idea that will impact all of our culture.' "

While he was out jogging and praying one day, the idea for "Fireproof" came to him. He footed it over to his brother's house about a mile away and told him the story: A firefighter who lives by the mantra "never leave your partner behind" at work is about to do just that in his personal life.

The movie, which has a strong faith-based message and was made with a budget of just $500,000 and a volunteer cast that includes former teen idol Kirk Cameron, has been surprisingly successful. Its opening on 839 screens two weeks ago was strong enough to propel it to No. 4 at the box office. It stayed in the top 10 last weekend, at No. 8, and has earned an estimated $13.6 million and spawned a best-selling book that started as a prop. It continues playing in Honolulu this week.

"Religulous," Bill Maher's jeremiad zinging religion, was No. 10 in its debut last weekend.

In "Fireproof," Caleb Holt (Cameron) receives the book from his father, who tells him to follow its 40-day challenge to save his marriage.

Prompted by repeated questions during production about whether the book really existed, the Kendricks sat down last spring and prayed to God to help them write it.

"It's an answer to prayer. I don't think I'm smart enough to come up with something like that on my own," Alex Kendrick said in a telephone interview. "I do think these are legitimate principles and not something we pulled out of thin air."

The brothers said the overwhelmingly positive response to the film has been rewarding and cited the more than a thousand e-mailed stories posted on the movie's Web site from people who have seen it and been affected by it.

They acknowledged the movie is not as artistically or technically fancy as many films out of Hollywood, but say its appeal is its relatable message that things aren't always easy but marriage is worth fighting for. That message is conveyed by the title, which takes on a double meaning given that the main character is a firefighter.

"It doesn't mean when something is fireproof that fire will never come, but when fire comes, it can withstand it," Alex Kendrick said. "Every marriage will go through trials, or fire, as we say, and what's going to happen on the other side of that fire? Will your marriage survive?"

IN THE BEGINNING

The Kendricks grew up in suburban Atlanta and now live in Albany in southwestern Georgia, where they are associate pastors at Sherwood Baptist Church. Along with the church's senior pastor, Michael Catt, they created Sherwood Pictures, a production company, in 2002 and scraped together $20,000 to put out their first film, "Flywheel," in 2003.

With a budget of $100,000, the company released "Facing the Giants" in 2006. That film ended up grossing more than $10 million. Cameron, best known for the TV sitcom "Growing Pains," saw the film and called the Kendricks to say he loved it and would be interested in working with them.

After auditioning several actors for the role of Caleb, the brothers decided to give Cameron a call, but they were skeptical. They saw the lead as a big burly guy, but Cameron flawlessly executed nine of the script's most difficult scenes during his audition and won them over.

Cameron, who turns 38 Sunday and has six kids after 17 years of marriage, said he is very aware of the challenges of marriage and wanted to be a part of something that encourages people to fight for that union.

"This is a movie that gives people hope and inspires them that they can save their marriages — that love, in the end, won't fail, if you pour your heart and your time and your energy into the things that really matter," Cameron said.

VOLUNTEER CAST

The rest of the cast was made up of volunteers from the church. Most of the budget was spent on equipment and paying a handful of professionals to operate that equipment. The Kendricks, who plan to continue making films, wrote the script together, and 38-year-old Alex directed and edited the film, while 35-year-old Stephen worked as a producer. Catt served as executive producer.

Part of the film's success can be attributed to a marketing plan that targeted areas with large and enthusiastic faith-based communities. Distributor Samuel Goldwyn Films had a pretty good idea of where it might do well based on where "Facing the Giants" succeeded, said head of distribution Michael Silberman.

It has done best so far in the Atlanta region as well as cities such as Dallas, Tampa, Fla., Orlando, Fla., and Charlotte, N.C., Silberman said.

A marketing technique honed during the "Facing the Giants" release, the "action squad," helped bring the movie to some smaller markets that might not otherwise have seen it on opening weekend. If the film wasn't set to play within 30 miles of a community, an action squad could bring it there by buying 1,000 tickets.

The success may also be driven by the fact that the Christian community, including the Kendricks, is also starved for movies that reflect its values, which often is not the case with Hollywood fare.

"We want to go enjoy good movies, but we rarely ever see the kind of movie that we have been longing to see, where there's a moral message that's communicated, it's clean, you can watch it with your kids, your wife, your grandmother, but you can laugh and cry and be entertained," Stephen Kendrick said.

Associated Press writer Erin Carlson in New York contributed to this report.⁡