This movie is another powerful exhibit in the case for why there *should* be an Oscar category for Best Casting.
Apart from Mr. Duvall's identifying acting, so rightly hailed elsewhere on this forum, what truly makes this film stand out as so genuine, so founded, so real, is the casting.
Take the radio guy, right down to his supermarket-style glasses. Take the Rev. Blackwell, fighting to hold back his bursting enthusiasm for Jesus so as not to have another heart attack. Take the talkative lady who almost clashes with the fat woman with twins - haven't we seen them both in our churches? Take the Church Board representatives at the beginning of the film, I feel like I know a few like them! Take the elderly gentleman with the trumpet, struggling to play but doing it from his heart, I've seen it. And in the midst of it, enter mega-star Billy Bob Thornton - blending into the mix just like one of the rest. Bottom line is, there is simply not one character that doesn't come across as believable simply by *being* there, even before you see them act.
Academy, awake, let there be a Casting Category now.