Ephesians 2:19-21
19 Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God;
20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
21 In whom all the building fitly framed together groweth unto an holy temple in the Lord:
22 In whom ye also are builded together for an habitation of God through the Spirit.
In Spanish, instead of ‘chief corner stone’ he is referred to as the ‘principal angle stone’. In either way of looking at it, the first corner stone laid for a building determines both the location of the building and the direction in which it is oriented. All other parts of the building are oriented, or referenced, to that first corner stone. Without that stone, or rock if you will, the building has neither place nor direction. Perhaps another way to say it is without Christ there is no Christianity. The gospel would not exist without Him. Christianity would have neither place nor direction.
Similarly, we have The Book of Mormon. From the Introduction of The Book of Mormon:
Concerning this record the Prophet Joseph Smith said: “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.”
I was born and raised in Pennsylvania, along the Susquehanna River. That’s the same river where the priesthood and baptism were reinstituted to our church in this dispensation. Pennsylvania is also where most of The Book of Mormon translation took place. If you’ve ever gone to the visitor center the church has near the town previously known as Harmony, now called Oakland, you would note how all of these early events took place within a short distance from the river. Pennsylvania is called ‘the keystone state’, a moniker that reaches back to colonial days. As one of the original 13 British colonies in America, and later as one of the 13 states, it is physically between the northern colonies with more industrial economies formed by New York and New England, and the southern colonies that were more agricultural producing raw materials for the North and for export. Pennsylvania then and today has both a large industrial base and lots of farmland.
I'm told that an arch is the strongest architectural device in holding up building walls and roofs. In fact, it is the arch that gives the discipline architecture its name! The keystone is the upper-most and center stone in an arch. Remove the keystone and the arch falls along with any walls or roof it was meant to hold up. Just as if you remove Christ then all of Christianity falls, so too if you remove The Book of Mormon, then The Church of Jesus Christ of Latter-day Saints falls. We claim it to be given through a modern prophet of God. If The Book of Mormon is false, then Joseph Smith is a false prophet. If it is true, then Joseph must be a true prophet, and the church established through him must be a true church, the true church.
Just as no stone building stands without a chief cornerstone or keystone, so too all we latter-day saints believe rests on the chief cornerstone of Jesus Christ, and the keystone of The Book of Mormon.