There was no altar call at the end of the critically acclaimed mystery-thriller "The Constant Gardener," but I am sure that many people walked out of it converted to, or at least strengthened in, a belief that evil pharmaceutical companies are ravaging the African countryside.

"The Wedding Crashers" – which just crossed the $200 million mark – had no redeeming moral value; but snickering audiences surely emerged feeling a little better about their own promiscuous behavior. If you can laugh at it, how serious can it be? These are movies, not sermons, yet their persuasive appeal to certain audiences is undeniable. Think what you will, these movies work. And they do so because they have not forgotten (though, unfortunately, many Christian filmmakers have) what fiction films are supposed to do.

Flannery O'Connor, in her essay "Novelist and Believer," criticizes Christian novelists (and I would extend the same to Christian filmmakers) for overreaching: "We are not content to stay within our limitations and make something that is simply good in and by itself. Now we want to make something that will have some utilitarian value. Yet what is good in itself glorifies God because it reflects God. The artist has his hands full and does his duty if he attends to his art. He can safely leave evangelizing to the evangelists."

Good art is evocative; bad art doesn't trust the audience to "get it" on their own. Two films by Christian filmmakers, both released this month, provide a good comparison – not only of what works and what doesn't, but also of the role of the audience in the persuasive process.

"Exorcism" and "Echoes"

"The Exorcism of Emily Rose" – part courtroom drama, part horror film, about a priest on trial for negligent homicide as a result of an unsuccessful exorcism – is a pretty good movie. "Echoes of Innocence," the limited-release mystic, pro-chastity, romance, horror film that debuted the same day, is not. Granted, "Emily Rose" has a bigger budget and some well-known actors on board. But that can't be the only reason for its success – "My Big Fat Greek Wedding" was shot for $5 million (a pittance in the world of Hollywood) and ended up grossing nearly $370 million worldwide.

"Emily Rose," despite what some may think of its theology, manages to earn one of the highest accolades a film can get – it is provocative. "Echoes of Innocence," despite good acting from its lead, Sarah Simmonds, and her gal-pal, standout Natali Jones, is so intent on beating its audience over the head with its utilitarian, pro-chastity message that the rest of the film is a mess.

"The Exorcism of Emily Rose" understands the first rule of the cinema – you must entertain. The film introduces, albeit briefly, a winsome, devout Catholic college girl and then turns her world upside down when she is oppressed, and then possessed, by demons. Scott Derrickson and Paul Harris Boardman know they are making a horror film, and they deliver on that genre's requirements (though much more subtly and believably than other films in this niche). Stuff happens on screen, people in the audience scream, but that's not all. The courtroom scenes realistically allow the importation of propositional truth and its disputation. And while a jury renders a verdict, and a judge imposes sentence, the audience is free to agree or disagree, which is exactly what happens when they leave the theater. The film's visuals and story line amazes them (and, in a sense, amuses), but afterward it engages.

"Echoes of Innocence," by contrast, is so full of undeveloped plotlines and heavy-handed characters that audiences are not free to discuss whether saving one's sexuality for marriage is a good idea. Don't get me wrong – it was refreshing to even consider a film that appeared to champion chastity, and a scene in which one young woman is seduced and later tries to repent is both laudable and moving. But Sarah, the innocent virgin, is so universally loathed by her classmates for her stance on chastity that the film might accidentally reinforce the commonly held, but demonstrably false, idea that "everybody's doing it." And it is not enough for the bad guy to be a high-school aged sexual predator – a common enough real-world character – instead he must be demonically possessed. Sarah's virginal body becomes a literal spiritual battlefield where one false step (a ridiculously small one, as it turns out) will send her into the confines of hell forever.