After the parenthetical clarification of the Moses prophecy, Joseph returns to the topical prophecy, that of the future Joseph. This new Joseph would bring forth the word of God, and would be a power for conversion, not just the presentation of the word. The last phrase "which shall have already gone forth among them" refers to the Bible. Joseph Smith would bring forth the Book of Mormon, and have power to convert also through the word of God as found in the Bible.