"God's Not Dead," an independent, Christian-based drama about a college student who debates the existence of God with his atheist philosophy professor, was unexpectedly popular this weekend; in fact, it ranked No. 5 at the box office.

The film, which includes no big-name actors (though "Duck Dynasty" stars Willie and Korie Robertson appear as themselves in the movie) earned $8.6 million despite opening in only 780 theaters, according to Adam Markovitz at Entertainment Weekly. The film benefited from social media marketing (over 1 million people have "liked" "God is Not Dead" on Facebook) and promotion at Winter Jam, a Christian music festival, Markovitz said.

Gary Susman at Moviefone provided four reasons for the film's success: Multiple church groups bought tickets in advance, it is set in contemporary times (which Christian movie audiences seem to prefer over period pieces), it appeals to Christians who feel mainstream culture is not faith-friendly and it opened on a weekend when other religious movies were not strong contenders ("Son of God" is not performing strongly and "Noah" doesn't hit theaters until next week). Furthermore, "Divergent" and "Muppets" did not perform as well as expected, Susman said.

Willie Robertson recently told the Christian Post that the movie "raises the bar."

"I've seen some Christian movies where the acting's not as good or the story's not as good, or it's just a lower budget film," said Robertson, adding the film's plot is "very compelling."

Actor Kevin Sorbo, who plays the atheist professor in the film, hopes "God's Not Dead" will create discussion, according to The Blaze. He also hopes the film will convert agnostics.

"Agnostics out there who kind of believe, kind of don’t … these are the independent voters," said Sorbo. "We want them to come over to the right side."