Modern-day revelation explains this verse as follows: “What is the root of Jesse spoken of in the 10th verse of the 11th chapter? Behold, thus saith the Lord, it is a descendant of Jesse, as well as of Joseph, unto whom rightly belongs the priesthood, and the keys of the kingdom, for an ensign, and for the gathering of my people in the last days” (D&C 113:5–6). In a related topic, Elder Bruce R. McConkie states also: “Christ is the Root of David. (Rev. 5:5; 22:16.) This designation signifies that he who was the Son of David was also before David, was pre-eminent above him, and was the root or source from which the great king in Israel gained his kingdom and power” (Mormon Doctrine, 2d ed. [Salt Lake City: Bookcraft, 1966], 657).
Consider also the expression “a rod out of the stem of Jesse” (2 Nephi 21:1; Isaiah 11:1) in terms of this additional statement from modern-day revelation: “What is the rod spoken of in the first verse of the 11th chapter of Isaiah, that should come of the Stem of Jesse? Behold, thus saith the Lord: It is a servant in the hands of Christ, who is partly a descendant of Jesse as well as of Ephraim, or of the house of Joseph, on whom there is laid much power” (D&C 113:3–4).