Third Nephi in the Book of Mormon tells of a visit Jesus Christ made to the American peoples after his crucifixion. The address given to the American people is similar to the Sermon on the Mount found in the Bible. There is one key difference that takes place at the end. Three Nephites are asked to approach Jesus, who tells them that they will live among the people of the world until his return. Part of the promise is that the people of the world will be unaware of their presence.
The Book of Mormon does not mention the Three Nephites again, but this otherwise obscure passage has been the basis for many Mormon folktales. The Light Planet web site discusses the Mormon folklore stories and the typical form they usually take. The text of the Book of Mormon mentions only that they shall live among the people of the world and that no one will notice their presence.
The typical pattern of the Three Nephite tales in Mormon folklore is that a mysterious stranger shows up, offers help, and then disappears. At times the recipient of such help may be offered a test to prove his worthiness, but the major feature is that the Nephite is never seen by that person again. These stories often are similar to miracle stories told by Catholics, and stories of the prophet Elijah that were common in Palestine in the first century A.D, according to the Light Planet web site.
The Three Nephite stories follow an older pattern established by other religions, but the Three Nephites are figures that appear only in Mormon folklore, largely because Mormons are the only religion to believe in them. Similar stories can be found involving John the Revelator, who also walks the Earth waiting for the Second Coming of Jesus Christ.
The stories of the Three Nephites serve to offer comfort and bolster the faith of the believer. The truthfulness of these stories, although they may be told fervently, cannot be easily verified, although it may be interesting that similar stories with different figures are told by members of different religions. The Three Nephites may still be roaming the world without the world knowing of them as the Book of Mormon suggests, but the stories told about them are an cultural phenomenon.
Resources:
Encylopedia of Mormonism – Mormon Folklore