The amen ends Mormon’s inserted testimony and declaration. What he has declared is that he is a disciple, or apostle, and that he has a mission to spread God’s word. He is doing that through what he writes, but he also knows that what he writes is for some future generation. Therefore, at the end of his insertion, his thoughts turn to the house of Jacob to which his people will eventually be reunited and reconciled. Nephi spent time thinking of, and preaching about, the restoration of the House of Israel. Mormon, at the end of the Nephite nations, thinks, and writes, of the same thing: “surely as the Lord liveth, will he gather in from the four quarters of the earth all the remnant of the seed of Jacob.” Mormon ends with his apostolic declaration: “then shall they know their Redeemer, who is Jesus Christ, the Son of God.”
This ends a chapter in the 1830 edition of the Book of Mormon.