Verse 9 begins by declaring: “This is written for the intent that ye may believe that.” The word that refers to Jesus Christ and his gospel, referenced in the preceding verse. Thus, Mormon again declares that the purpose of the Book of Mormon is to be a witness to Jesus as the Christ, the Son of God.
His final declaration to the future Lamanites is to assure them that they are “a remnant of the seed of Jacob; therefore [they] are numbered among the people of the first covenant.” That means that all of the blessings of the covenant can pertain to them—“if.” The “if” is that “[they] believe in Christ, and are baptized, first with water, then with fire and with the Holy Ghost.”
These are Mormon’s last words, and the end of a chapter that originally included our Chapters 5–7.