The 42-year-old former teen idol has described the movie as his "most personal" project to date.
"Kirk goes back to the beginning -- literally -- as he investigates the origins of good and evil and how they impact our lives... and our eternities," a synopsis on the film's website said. "Reminding us that there is great hope, 'Unstoppable' creatively asks -- and answers -- the age-old question: Where is God in the midst of tragedy and suffering?"
The documentary earned $2 million during its initial Sept. 24 screenings at 700 U.S. theaters, box-office records show. More than 150,000 tickets were sold for the NCM Fathom Events presentation of "Unstoppable," which was arranged in partnership with Provident Films, and averaged almost $2,900 per screen in its opening, when Cameron spoke to audiences via video link from The Vines Center at Liberty University in Lynchburg, Va.
An encore presentation of the film, accompanied by Cameron's presentation, is scheduled for Thursday in more than 660 movie theaters.
"It was exciting to see that a little movie like 'Unstoppable,' about a very potentially unmarketable topic -- something that could potentially be sad and depressing -- turned out to be No. 1 at the box office last Tuesday, beating out Hugh Jackman's movie 'Prisoners.' And you think, 'Why in the world would something like that happen?' And I think it's because there are millions of people who feel their values are not represented in Hollywood and they want to see things like this about faith, hope and love," Cameron told United Press International in a phone interview this week.
"I think they want to be part of something that changes the culture and that's very encouraging to me. I think it's kind of like the momentum changing in a football game. People say, 'We can do something; we do have a voice and we want to shape the world that we live in.'"
Interest from audiences and the media grew after Cameron said Facebook and YouTube initially blocked the film's trailer, labeling it as "unsafe" and "abusive."
Cameron's supporters immediately rallied online support and the trailer was reinstated, with representatives from the websites explaining the trailer was mistakenly flagged as violating their regulations against spam.
Asked if he expects as big a turnout Thursday as his film received last week, Cameron replied: "I hope so. We're doing everything we can. ... We would love to pack the theaters again Thursday. We tell people: 'Even if you've seen the film, bring your friends who really might be struggling with this question and it might be keeping them from having a deep, abiding faith in God.' And we're hoping people use this as a tool to help people they care about."
Best known as the star of the 1980s sitcom "Growing Pains," Cameron is a married father of six children whose career focuses on acting in spiritual-themed films, such as the 2008 hit "Fireproof." He also is active in the evangelical Christian ministry The Way of the Master.