The Book of Mormon, Faith, and Morality
Kevin Price is a devout Mormon. He's the very picture of faith and devotion. He's smart, polite, confident, and charismatic, and he believes in his religion and his God absolutely and unconditionally, as he demonstrates in "I Believe". He has a powerful conviction and strength of belief; however, instead of thinking about others, he's focused on gaining glory for himself. He's more interested in doing "something incredible" than in actually helping people. Kevin's belief is strong, but blind; he knows what he's been taught, but he doesn't truly understand it.
More to the point, why do you let bad things happen to me?
I know you don't think I'm a flake
But you've clearly made a mistake
I'm going where you need me most: Orlando!
Arnold Cunningham is more or less the opposite. He's shy and socially awkward—a follower, not a leader. He hasn't even read his own holy text, and he isn't totally clear on a lot of it: he frequently gets it confused with The Lord of the Rings and Star Wars, and he thinks "latter day" means "tomorrow". However, Arnold is genuinely kind and caring, and always puts himself last. He takes a Broad Strokes approach to his religion: he may not be able to quote chapter and verse, but he's pretty sure that God doesn't want you to rape babies.
This explains why Elder Cunningham succeeds at converting the Ugandans where Elder Price fails. Elder Price thinks all he has to do is believe hard enough and everyone will line up to follow him, but his evangelizing is rigid, unfiltered, and, ultimately, irrelevant to his audience. If your strategy is to read The Bible out loud, cover to cover, it doesn't matter how loudly you shout it or how hard you believe in it...you're not going to convert anyone. In contrast, Elder Cunningham blatantly makes things up, and as a result, his preachings are flexible and holistically appealing to his audience. It doesn't matter that his preachings aren't, technically, accurate—he's lifting their spirits and helping them to become better people. Elder Price understands the letter of Christ's teachings, but it's Elder Cunningham who understands the spirit.
In the end, Arnold's loose interpretation of his religion converts the villagers, defeats the warlord, and makes everyone better off than they were before, proving for all involved that what matters isn't whether or not you believe the stories are true—it's whether believing in them makes you a better person.