“Chapter 54: The Promise of the Book of Mormon,” Book of Mormon Stories (1997), 156
Before Moroni buried the plates for the last time, he wrote a promise to the Lamanites and to anyone else who would read the records.
He told people to read the records, really think about them, and then ask Heavenly Father if they are true.
Moroni promised that if people would ask sincerely, with faith in Christ, the Holy Ghost would help them know the records are true.
Moroni wrote that if people repent, follow Jesus Christ, and love Heavenly Father, they can become perfect.
When Moroni finished writing on the gold plates, he hid them in a stone box in the Hill Cumorah and covered the box with a big rock. His mortal work was finished.
Mormon 8:4; Joseph Smith—History 1:52