The two-year mission is a rite of passage for most young Mormon men.
"We get new missionaries every six weeks," said Baton Rouge Mission President Jim Wall, "and every six weeks, we have missionaries go home. And the contrast is incredible."
The Church of Jesus Christ of Latter-day Saints is one of the fastest growing religion in the U.S., and more than 55,000 missionaries serve throughout the world. For the most part, they are young men about 20 years old. For "Nightline," the LDS church gave ABC News' Bob Woodruff rare behind-the-scenes access to missionaries in Louisiana over a two-day stretch that included door-to-door proselytizing, work on service projects and teaching.
Watch the full story on "Nightline" tonight at 11:35 p.m. ET
"I've been a missionary for 20 months, knocked on countless doors, talked to countless people, and the excitement does not go away," said 20-year-old missionary Elder Bert Curtis, while walking the streets of LaPlace, La.
"Elder" is a church term, and Elder Curtis arrived in the bayou from his home in Utah knowing little about what to expect.
"People always told me, 'You're going to have jambalaya and gumbo, it's going to be great,'" he said. "I was like, 'What is jambalaya and gumbo?'"
Missionaries pay most of their own way, amounting to $400 a month, and have no say on where they serve. The church determines -- Mormons believe in divine guidance -- where missionaries are placed. Presidential hopeful Mitt Romney spent his mission in Bordeaux, France, where he has said he learned about rejection in trying to convince the French to give up wine.
Elder Curtis said that he has come to realize that Louisiana is the right place for him.
"I wasn't called to do something or learn a language," he said, "because that's not what it's about. I was called to a specific group of people. I was called to teach people of Louisiana."
Elder Curtis' day starts by 6:30 in the morning and lasts well past dark. He is paired with another missionary, Elder Zachary Dustin, 21. They are required to stay by each other's sides. All missionaries work in pairs.
"We call that sight and sound. It's just for safety's sake," Wall said. "When they started their missions, they had this desire to be really helpful and serve, but somebody didn't wave a magic wand and take away all the dumb. Once in a while, they make bad choices. When you're with a companion, it's harder to make really bad choices."
Like all Mormons, they are not allowed to drink alcohol, coffee or tea. The missionaries also do not return home for the entire span of their mission, and they can only call home twice a year, on Mother's Day and Christmas.
"I miss my family more than anything in the world, and it's the hardest thing I've ever done to be away," said Elder Dustin, "but ... those feelings have been able to be totally submerged in serving."
As Elders Curtis and Dustin wandered the streets of LaPlace, going door-to-door to talk to strangers about their religion, some of the people they encountered were receptive to them and wanted to share feelings about Jesus Christ, but others were not.
"We have our own religion," said one woman, who then refused to take a pamphlet from them.
LaPlace is about halfway between New Orleans and Louisiana in St. John the Baptist Parish, in a deeply religious part of the South where Mormons are relatively scarce.
"I think that there's a lot of people who have faith in Christ," said Elder Curtis, "and sometimes maybe it's our fault, maybe it's something they've heard, but for some reason they don't understand that we're trying to add to that faith in Christ."
Mormons believe there is additional biblical scripture called the "Book of Mormon" that details Jesus' visit to the ancient Americas after his resurrection. According to Mormons, this text was discovered by the prophet Joseph Smith in the 1820s buried underground on golden plates in upstate New York.
"We believe that our church has been given authority from God to act in his name," Wall said. "And that authority is recognizable, and that's what we try to teach."