Some religious people might ask why I would make such a movie and emphasize that this evangelical preacher has weaknesses. And my answer is that we either accept weaknesses in good people or we have to tear pages out of the bible. I would have to rip the Psalms out of the bible and never read them again. Because no one less than the greatest king of Israel, King David, the author of the Psalms, sent a man out to die in battle so that he could sleep with his wife. And that was a far more evil thing than anything Sonny would ever, ever do.Duvall's interest in portraying this distinctly American brand of Christianity was born from an encounter with a Pentacostal preacher in Arkansas more than thirty years ago. Regarding other attempts at depicting the Pentacostal tradition, Duvall comments "They patronize . . . They put quotation marks around the preacher. They don’t give the minister or his congregation their due." The Apostle, however, can be commended for a realistic depiction of religious faith refreshingly free of such condescension.
I was initially drawn to the film upon learning that Duvall not only wrote the script, directed the film, and starred in it himself, but put up 5 million of his own money to produce it himself. Here's an interview with Robert Duvall from the University of Nebraska's Journal of Religion and Film on his inspiration for making "The Apostle".
(Thanks to David Mills from Mere Comments for the link).