When the republican national convention kicks off four days from now, a prayer will be offered on the final night by a mormon bishop. As we said, last night, for the first time in american history, a... See More
When the republican national convention kicks off four days from now, a prayer will be offered on the final night by a mormon bishop. As we said, last night, for the first time in american history, a mormon will be nominated for the highest office in the land. And since so many people regard the faith as a mystery, abc's dan harris returns tonight with a rare tour of one of the most sacred and private mormon temples. Reporter: We've all seen the outside of the temples but very few get to go where I went, inside. And this is one of the first rooms I saw. The celestial room. Intensely ornate, it is meant to evoke the peace and tranquility of heaven. In the temple, mormons wear all white in order to enter. A mormon must be deemed chase and must be contributing 10% of their income to the church. You are now looking at the room where the faithful stand in that pool which is heated and chlorinated and are baptized in the name of the dead so they can have the option converting to mormonism in the after life. Those oxen represent the 12 tribes of israel. My guides on this tour are two of the church's 12 apostles. Top officials who are believed to be prophets, seers and rev laters. Elder russell ballard. We know the voice of the lord. We know when he want it s us to do something. Reporter: They were willing to discuss their rituals to a point but they would not address rumors of things like secret handshakes. You're not supposed to talk about the details? We don't get into the details of that. You're going through a process that, which taken out of context, can seem unusual or different. But in the whole context doesn't seem that way at all. Reporter: Two other aspects of the faith that outsiders tend to focus on are polygamy, which every mormon will be quick to tell you was outlawed more than a century ago, and the special undergarments that mormon men and women wear every day which we're not showing here because mormons are sensitive to their display. They describe them as simply tangible representations of their faith. But the real center of their faith, say mormons, is something much larger, the family. You are looking now at the ceiling room where weddings take place. Mormons don't just get married, they are sealed for eternity, to be at the highest level of heaven, you need to be married. This professor, a practicing mormon and author of the upcoming book "a peculiar people." It is a family-oriented vision of the after life. The significance of that view of heaven dictates a kind of family centeredness. Here in what mormons call mortal life. Reporter: Which is why t two-thirds of mormons are mar married compared to about half of the rest of the population. Mormon women are twice as likely to describe themselves as housewives. He appeared to joseph smith. Reporter: Once a week, mormon families like the aherns of pennsylvania are expected to hold something called family home evening. A way to be happy in our families. Reporter: No phones, no tvs, no computers. Just food, song, prayer, games and lesson. The most important part is just having our children know that we love them and love spending time with them and that we're a family that is staying together. Reporter: All of it, says professor flumin, proof of how the mormon faith is both very different and very demanding. Mormonism tends to define life in various ways for a practicing latter day saint. Tends not to be an element of one's life but an all encompassing life choice. It's not a faith that's worn lightly. Fascinating tour. But how does a nonmormon get a tour? How did you get in? So this was a new temple. Before they closed the doors officially to outsiders, they let us in. What did they say about why they don't let outsiders come in all the time? Their argument is it's not so much that it's secret but that it's sacred. What they're doing in there is holy. Then say only the mormon faithful should be allowed in. They also say it's the fastest growing religion in the world. It's about 1.7% of the american population, roughly equal to the juews. They argue it's growing worldwide. They have an army of 50,000 missionaries, most of them young people, all over the planet. One of their young missionaries several decades ago was a young man by the name of mitt romney. About to be nominated for president. Thank you, dan harris.
This transcript has been automatically generated and may not be 100% accurate.