We do not know when in Moroni’s life he wrote the Title Page of the Book of Mormon. It was certainly after he had edited Ether. Although there is no indication that it was written after Moroni 10, it would seem a fitting ending. Moroni, Chapter 10, is Moroni’s personal testimony to future generations, and the Title Page gives the Book of Mormon’s orientation to them.
Regardless of the timing of the Title Page, this is Moroni’s final testimony. It is not a testimony of the book, but a testimony of Christ. His exhortation is not focused on believing the book, per se, but on believing the purpose of the book: to “come unto Christ, and be perfected in him.”
Verse 34 indicates that Moroni is finally arriving at a time when he can see the end of his days. Therefore, he can write no more. Therefore, it is time to seal up his work and commit it to the future.
As he noted in verses 27–29 of this chapter, there will come a time when Moroni will stand with God to meet us and discharge his final task as witness to the Book of Mormon, and to Christ.