Nephi implies that his calling and election has been made sure (v. 6). If only this verse were read it may seem to be just a general statement about the Atonement of Christ, but his comments in verse 7 about charity extends the general meaning to one about Nephi specifically. Charity is the requirement for becoming like Christ and attaining the Celestial Kingdom.
46 Wherefore, my beloved brethren, if ye have not charity, ye are nothing, for charity never faileth. Wherefore, cleave unto charity, which is the greatest of all, for all things must fail—
47 But charity is the pure love of Christ, and it endureth forever; and whoso is found possessed of it at the last day, it shall be well with him. [Moroni 7:46–47]
Nephi has charity for three groups of people to whom he knows his words will go: the Lamanites, the Jews, and the Gentiles (see comments, 2 Nephi 30:4 concerning Nephi being a Jew, v. 8). All three of those groups must be reconciled to Christ. This is why the Book of Mormon was written. Every person in any of these three groups must follow the plan of salvation that Nephi explained in 2 Nephi 31. He again summarizes them here: (1) Enter the narrow gate (have faith and repent and be baptized); (2) walk in the straight path that leads to eternal life (join the Church and follow its teachings as guided by the Holy Ghost); and, (3) endure to the end of their mortal probation (be faithful unto the end) (v. 9).
Nephi does not address the lost tribes whom he had previously said would receive the words of his seed (the Book of Mormon). He probably didn’t because he knew or felt their receiving Nephi’s record would not be until the millennial reign or just before (see 3 Nephi 21:23–26). The Lamanites, Gentiles, and at least many of the Jews would receive it before the millennium.