This righteous branch was Lehi’s family. JST for Gen 50:25 reads, a branch shall be broken off, and shall be carried into a far country.
Lehi continues to explain that the Messiah should be made manifest unto them in the latter days, in the spirit of power, unto the bringing of them out of darkness unto light. One might be tempted to interpret this as having reference to the appearance of Christ to the Nephites and Lamanites. However, the Messiah is manifested “in the spirit of power,” or by the Holy Ghost. In other words, the Lord would be manifested to the descendants of the branch of Lehi when the Gentiles of the last dispensation would take the gospel to the American Indians. The Lord can be made manifest to a people without physically appearing to them. The Gentiles of the early Christian era learned of the Messiah in this way, they understood me not that the Gentiles should not at any time hear my voice—that I should not manifest myself unto them save it were by the Holy Ghost (3 Nephi 15:23). This interpretation is more consistent with the context of the next verse which speaks of the mission of Joseph Smith.