"We believe in the literal gathering of Israel and in the restoration of the Ten Tribes; that Zion (the New Jerusalem) will be built upon the American continent; that Christ will reign personally upon the earth; and, that the earth will be renewed and receive its paradisiacal glory," Article of Faith 10.
Jacob the son of Abraham had 12 sons: Reuben, Simeon, Levi, Judah, Issachar, Zebulun, Dan, Naphtali, Gad and Asher, Joseph, and Benjamin. Reuben lost his birthright because of grievous immorality. The birthright was then given to Joseph,1 Chronicles 5:1–2. Levi, whose tribe the Lord chosen to serve as his priesthood ministers, did not receive an inheritance because of their special calling to minister among all the tribes. This allowed Joseph’s double portion to be shared by Joseph’s sons, Ephraim and Manasseh, 1 Chronicles 5:1; Jeremiah 31:9, who were separate tribes of Israel. For a complete history of who the twelve and ten tribes were by the time they were led away, read this article.
The Ten Tribes, are the some of the families descended from Jacob (Israel) of the Old Testament, who were scattered over the face of the Earth through conquest and other means. When missionaries teach people all over the earth about the gospel of Jesus Christ, they participate in the literal gathering of Israel into the fold of Jesus. As the Prince of Peace, Jesus will return to an earth restored to beauty and peace during the millennium to reign and rule. To modern ears, this may seem like nonsense. I'll never forget the first time I learned this doctrine and how its truth burned into my heart. It is true and nothing can shake my testimony of it.
"For, lo, I will command, and I will sift the house of Israel among all nations, like as corn is sifted in a sieve, yet shall not the least grain fall upon the earth," Amos 9:9
"That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him," Ephesians 1:10
"And he will lift up an ensign to the nations from far, and will hiss unto them from the end of the earth: and, behold, they shall come with speed swiftly," Isaiah 5:26
"I will say to the north, Give up; and to the south, Keep not back: bring my sons from far, and my daughters from the ends of the earth," Isaiah 43:6
"Therefore, behold, the days come, saith the Lord, that it shall no more be said, The Lord liveth, that brought up the children of Israel out of the land of Egypt; But, The Lord liveth, that brought up the children of Israel from the land of the north, and from all the lands whither he had driven them: and I will bring them again into their land that I gave unto their fathers. Behold, I will send for many fishers, saith the Lord, and they shall fish them; and after will I send for many hunters, and they shall hunt them from every mountain, and from every hill, and out of the holes of the rocks," Jeremiah 16:14-16
"Him that overcometh will I make a pillar in the temple of my God, and he shall go no more out: and I will write upon him the name of my God, and the name of the city of my God, which is new Jerusalem, which cometh down out of heaven from my God: and I will write upon him my new name," Revelations 3:12
"The wolf and the lamb shall feed together, and the lion shall eat straw like the bullock: and dust shall be the serpent’s meat. They shall not hurt nor destroy in all my holy mountain, saith the Lord" Isaiah 65:25