Mormon expanded upon his fourth desire from verses 2–5, which was itself, a lucid summary of the mission of Jesus:
Mormon echoes here the words of Abinadi (which he would have been aware of), quoting Isaiah, regarding “the sting of death” being swallowed up in Christ (Mosiah 16:8; Alma 22:14). His listing of these elements of belief also track in style and content King Benjamin’s words (Mosiah 4:9–10), as well as the consistently repeated elements in the standard Nephite declarations of faith (compare especially 2 Nephi 9:4–15; Alma 33:22).
Mormon’s summary statement here and its expansion illustrates his sincere love for his people and his powerful testimony of the details of Christ’s Atonement. He wanted his people to know:
“to dwell in the presence of God in his kingdom, to sing ceaseless praises with the choirs above, unto the Father, and unto the Son, and unto the Holy Ghost, which are one God, in a state of happiness which hath no end.”
Then in verse 8, Mormon added literally the “therefore.” Because he knew, and (presumably by the nature of his description) had seen what lay ahead, he returned to his very forthright listing of what the people needed to do to attain this beautiful goal. They needed to “repent, and be baptized in the name of Jesus, and lay hold upon [and cling to] the gospel of Christ, which shall be set before you” (7:8).
John W. Welch and Greg Welch, “Consistent Elements in Nephite Declarations of Faith,” in Charting the Book of Mormon, chart 43.