"I told the Brethren that the Book of Mormon was the most correct of any book on earth, and the keystone of our religion, and a man would get nearer to God by abiding by its precepts, than by any other book".
(Joseph Smith, found in the Introduction to the Book of Mormon)
The divinity of the Book of Mormon is very clear in that statement by Joseph Smith. The symbolism of a keystone refers to an arch. Though an arch is made up of several wedge shaped stones called voissours, the top stone, or the keystone, is essential to the integrity of the entire structure. Without the keystone the entire arch would be unable to stand.