A big surprise at the box office this weekend was the 4th place opening of Provident/Samuel Goldwyn’s Fireproof, the small budget and limited release pic about a firefighter who recommits to his marriage and his faith. The movie is the latest from Sherwood Pictures, a nonprofit ministry of Sherwood Baptist Church in Albany, Georgia, that previously put out the popular Facing the Giants and the lesser-known Flywheel. Samuel Goldwyn Films is the theatrical distributor, while Provident Films handled Fireproof‘s outreach and marketing to Christian audiences. It debuted to a $2.3M Friday and $2.6M Saturday for a $6.5M gross weekend though released into only 839 dates and costing just $500K. The reason why is that the pic used grassroots methods to directly reach churches  on behalf of the PG film starring the grown-up star of TV’s Growing Pains, Kirk Cameron. (The evangelical actor claims he donated his pay from Fireproof to a camp for seriously ill kids he runs with his wife.) It had the year’s highest grossing opening weekend return of any film (except 3-D Hannah Montana) released on 1,000 screens or less. Faith-based “Action Squads” bought up blocks of tickets. “Just between you and me, keep your eye on the Fireproof per screen averages this weekend,” a source at Grace Hill Media, which markets to the religious community but wasn’t involved with this movie, tipped me. “On Sunday, I think there will be some distribution execs around town who will be asking ‘What the hell is Fireproof?’ ” The studios did.

But what’s interesting about the pic’s success is that not all Christian-themed movies do well: in fact, most don’t, especially those made by the majors trying to cash in on Mel Gibson’s blockbuster The Passion Of The ChristHollywood still can’t figure out what works and what doesn’t for faith-based audiences. Today, Fireproof is still going strong with advance ticket sales, accounting for the largest share — 22% — of all sold, according to big online ticketseller Fandango.com. “Because of the sold-out screenings and strong word-of-mouth, we expect next weekend’s ticket sales for this movie will be equally healthy,” spokesman Harry Medved told me.