The Lord’s commandment for Lehi’s sons to return to Jerusalem a second time was to eventually fulfill a blessing given by his father Jacob, who was the father of the twelve tribes of Israel. The blessing given to Joseph was:
22 Joseph is a fruitful bough, even a fruitful bough by a well; whose branches run over the wall:
23 The archers have sorely grieved him, and shot at him, and hated him:
24 But his bow abode in strength, and the arms of his hands were made strong by the hands of the mighty God of Jacob; (from thence is the shepherd, the stone of Israel:)
25 Even by the God of thy father, who shall help thee; and by the Almighty, who shall bless thee with blessings of heaven above, blessings of the deep that lieth under, blessings of the breasts, and of the womb:
26 The blessings of thy father have prevailed above the blessings of my progenitors unto the utmost bound of the everlasting hills: they shall be on the head of Joseph, and on the crown of the head of him that was separate from his brethren. [Genesis 49:22–26]
Joseph had two sons, Manasseh and Ephraim. Lehi “was a descendant of Manasseh” (Alma 10:3), and Ishmael was a descendant of Ephraim. The lineage of Ishmael comes from the Book of Lehi, according to Elder Erastus Snow, an earlier member of the Quorum of the Twelve.
Whoever has read the Book of Mormon carefully will have learned that the remnants of the house of Joseph dwelt upon the American continent; and that Lehi learned by searching the records of his fathers that were written upon the plates of brass, that he was of the lineage of Manasseh. The Prophet Joseph informed us that the record of Lehi, was contained on the 116 pages that were first translated and subsequently stolen, and of which an abridgement is given us in the first Book of Nephi, which is the record of Nephi individually, he himself being of the lineage of Manasseh; but that Ishmael was of the lineage of Ephraim, and that his sons married into Lehi’s family, and Lehi’s sons married Ishmael’s daughters, thus fulfilling the words of Jacob upon Ephraim and Manasseh in the 48th chapter of Genesis which says: “And let my name be on them, and the name of my fathers Abraham and Isaac; and let them grow into a multitude in the midst of the land.” Thus these descendants of Manasseh and Ephraim grew together upon this American continent, with a sprinkling from the house of Judah, from Mulek descended, who left Jerusalem eleven years after Lehi, and founded the colony afterwards known as Zarahemla and found by Mosiah—thus making a combination, an intermixture of Ephraim and Manasseh with the remnants of Judah, and for aught we know, the remnants of some other tribes that might have accompanied Mulek. And such have grown up on the American continent. [Journal of Discourses, 23:184–185]
The Lord was involved in getting the two families together. He softened the heart of Ishmael so he would go into the wilderness (v.5). Both branches of Joseph, Manasseh, and Ephraim, were brought to the utmost bound of the everlasting hills, the Americas, and became very fruitful in posterity. Of course there are many more of the posterity of Joseph that went with the ten tribes into Assyria and the North. The Lord said: “I will sift [scatter] the house of Israel among all nations, like as corn is sifted in a sieve” (Amos 9:8–9), and today they are and have been gathered out of many of those nations.