When the Book of Mormon was ready for printing in 1829, Joseph Smith's associates faced a practical problem. Sending the only manuscript into a printing shop meant it would be handled by compositors, spread across cases, and out of their control for months. Their solution was to make a second copy.
Oliver Cowdery, with two other scribes, wrote out the whole text between August 1829 and early 1830, and Egbert B. Grandin's shop at Palmyra, New York, set the first edition from that copy. The precaution turned out to be justified in a way nobody anticipated. The original dictation manuscript was placed in the cornerstone of the Nauvoo House in 1841, and when it was recovered in 1882 water had got in; only about twenty-eight per cent of it survives. The printer's manuscript is complete apart from a single leaf, and it is therefore the only substantially complete manuscript of the Book of Mormon in existence.
It has one further value that a printed edition cannot supply. The manuscript is almost entirely unpunctuated. Every full stop, comma and paragraph break in the 1830 edition was put there by the compositor, John Gilbert, working from an unpunctuated text. Anyone asking how the Book of Mormon is meant to be read is, at that level, reading a typesetter's decisions.