President Marion G. Romney has stated: “Whatever else it implies, this statement is amply justified by the fact that acceptance of the Book of Mormon is almost tantamount to acceptance of the restored gospel. The authenticity of the book and the restoration of the gospel rest upon the same two fundamentals—the fact of modern revelation and the fact that Joseph Smith was a prophet of God. These two verities are inseparably connected in their relationship to the Book of Mormon and the restored gospel. To accept one is to accept the other.” 
So, what it is about the Book of Mormon that makes it the fundamental keystone in our religion? In his book, A Witness and a Warning, Ezra Taft Benson highlights a few of the ways the Book of Mormon serves as the keystone of our religion. Along with President Benson’s insights, I have included below some of the thoughts and perceptions of other authoritative writers on this subject.
Above all, the Book of Mormon is the keystone of our witness to the world that Jesus is the Christ, the Son of the Eternal Father.
- The Keystone in Our Witness of Christ.
Much of the world rejects Jesus as their Savior and Redeemer. Many deny His divinity while others doubt His doctrine. But the Book of Mormon, in its clear and distinctive dialect, declares the truth of the divine mission and perfect life of our Lord and Savior.
“There is a God,” declares Nephi, “and he is Christ.” 
The Book of Mormon elucidates Christ’s sacred teachings and holy doctrines; it testifies of His atoning sacrifice. There can be no doubt that the Book of Mormon is an essential and necessary keystone in affirming to the world that Jesus is the Christ, the Eternal God.
- The Keystone of Our Personal Faith
President Ezra Taft Benson  further outlined the testimony of the Savior himself declaring that;
- The Book of Mormon is true, 
- It contains the word of God, 
- It was translated by power from on high, 
- It contains the fullness of the gospel of Jesus Christ, 
- It was given by inspiration and confirmed by the ministering of angels, 
- It gives evidence that the holy scriptures are true,  and
- Those who receive it in faith shall receive eternal life. 
Another essential element of the Book of Mormon is that it stands as the keystone of our doctrine.
- The Keystone of Our Doctrine
In ordinary language and easy to understand terminology, the Book of Mormon clarifies and illuminates all the essential doctrine necessary for our salvation. The Savior Himself has proclaimed that the Book of Mormon contains the "fulness of the gospel of Jesus Christ."  The Book of Mormon increases our understanding and knowledge of vital principles and doctrines which are essential to our redemption.
The Book of Mormon is also a critical keystone in our personal testimonies of the work of the restoration.
- The Keystone of Our Testimony
The Book of Mormon was written to convince us "that Jesus is the Christ."  If your soul is searching for a more profound witness of the divinity of our Savior, if you harbor any doubts or question any aspect of your testimony of the restored gospel, read the Book of Mormon. Ponder its message. Pray about its precepts.
The Book of Mormon is a powerful testifier of truth. It is a profound conversion tool. Above all else, you will "get nearer to God by abiding by its precepts, than by any other book." 
As you are brought to a realization of the truthfulness of the Book of Mormon, you will also come to know that Joseph Smith is the prophet of the Restoration and that the Church of Jesus Christ of Latter-day Saints is directed today by a living prophet.
In 1941, President Heber J. Grant affirmed that "experimental knowledge is the very best knowledge in the world; and any man who will believe what he is told to believe, in one of the closing paragraphs of the Book of Mormon, and who, after reading it, will ask God for a knowledge of its divinity, and live worthily of that knowledge will receive it.” 
The incredible conversion power of the Book of Mormon makes it a major keystone in our missionary efforts.
- The Keystone of Our Missionary Labor
As Heber J. Grant further explains; “I rejoice in the wonderful spirit of the Book of Mormon. I believe that it is one of the greatest missionaries in the hands of an elder that it is possible for him to have. I believe that no man can open that book and read it with a prayerful heart, and ask God, in the name of Jesus Christ, for a testimony regarding its divinity, but what the Lord will manifest unto him by His Spirit the truth of the book itself. And God has performed it; He has done it in thousands of cases. There is a mark of divinity on this book; and I maintain that no man can read [it]…without receiving an impression of this kind." 
Everyone who prayerfully studies the Book of Mormon can ask God if it is true and gain a testimony of its divinity. When, in answer to sincere prayer, the Holy Spirit testifies of the truthfulness of the Book of Mormon, then hearts are changed. People increase in faith and desire to unite themselves with the Kingdom of God.
- The Keystone of Our Lives
‘Behold, I speak unto you as if ye were present, and yet ye are not. But behold, Jesus Christ hath shown you unto me, and I know your doing.’ 
“If they saw our day and chose those things which would be of greatest worth to us, is not that how we should study the Book of Mormon? We should constantly ask ourselves, ‘Why did the Lord inspire Mormon (or Moroni or Alma) to include that in his record? What lesson can I learn from that to help me live in this day and age?’” 
The Book of Mormon is the keystone of our religion because it bears witness of our Savior Jesus Christ.
“Behold, I am Jesus Christ. I am the Father and the Son. In me shall all mankind have life, and that eternally.” 
It is the keystone of our religion because it teaches pure truth. Through modern-day revelation the Lord declares that the Book of Mormon contains “the fullness of the gospel of Jesus Christ”  and that "As your Lord and your God liveth it is true."  But there is something more to it that just these vital facts.
The Book of Mormon corroborates the truthfulness of the Bible.  It serves as verification "to the world that the holy scriptures are true.” 
Its earnest objective is to provide us with the necessary principles and teachings for our eternal journey. One of the ultimate messages of the Book of Mormon, and of the Bible, is that mankind cannot reach perfection on its own.
The Apostle Paul instructs us that, "The law was our schoolmaster to bring us unto Christ."  Abinadi taught that the records maintained by the Book of Mormon prophets (including the Brass Plates of Laban) served "to keep them in remembrance of God and their duty towards him." 
The Book of Mormon is our schoolmaster in this dispensation of time to bring us to Christ.  The book itself testifies that it is the holy word of God.
All scriptures are one in that they testify of Jesus. The prophet Jacob, brother of Nephi, declares that "none of the prophets have written, nor prophesied, save they have spoken concerning this Christ." 
Likewise, Nephi affirmed; "We talk of Christ, we rejoice in Christ, we preach of Christ, we prophecy of Christ." 
There is a very real and very tangible power associated with a sincere study of the Book of Mormon. As Ezra Taft Benson explains in A Witness and A Warning, its influence will begin to flow into our lives the moment we undertake a serious and sincere study of the truths and doctrines it contains. Our personal power to resist temptation will intensify. Our ability to elude deceptiveness will become more acute. We will become more adept at keeping our footing securely on the strait and narrow path.
President Marion G. Romney knew of the great power present in the Book of Mormon. He attested to the blessings available for those who will read and study the Book of Mormon:
“I feel certain that if, in our homes, parents will read from the Book of Mormon prayerfully and regularly, both by themselves and with their children, the spirit of that great book will come to permeate our homes and all who dwell therein. The spirit of reverence will increase; mutual respect and consideration for each other will grow. The spirit of contention will depart. Parents will counsel their children in greater love and wisdom. Children will be more responsive and submissive to the counsel of their parents. Righteousness will increase. Faith, hope, and charity-the pure love of Christ-will abound in our homes and lives, bringing in their wake peace, joy, and happiness" 
The promise of increased reverence and respect in our homes, the added blessing of greater love between parents and their children, as well as increased peace, joy and happiness are not imaginary inferences. They are, instead, precisely what Joseph Smith meant when he declared that the Book of Mormon will draw us nearer to God.
As President Benson explains, “The scriptures are called ‘the words of life,’  and nowhere is that more true than it is of the Book of Mormon. When you begin to hunger and thirst after those words, you will find life in greater and greater abundance.” 
 Smith, Joseph, History of The Church of Jesus Christ of Latter-day Saints, vol. 4, p.461.
 Romney, Marion G. Look to God and Live, GC Oct 1970.
 Title page, The Book of Mormon.
 2 Nephi 11:7.
 Benson, Ezra Taft, New Era, May 1975, p. 19.
 Benson, Ezra Taft, A Witness and a Warning, Deseret Book, Salt Lake City, Utah, 1988, p. 15.
 D&C 17:6.
 D&C 19:26.
 D&C 20:8.
 D&C 20:9, 42:12.
 D&C 20:10.
 D&C 20:11.
 D&C 20:14.
 Smith, Joseph, History of The Church of Jesus Christ of Latter-day Saints, vol. 2, p.52.
 D&C 20:9.
 Title Page, Book of Mormon.
Smith, Joseph, History of The Church of Jesus Christ of Latter-day Saints, vol. 4, p.461.
 Grant, Heber J., Gospel Standards (1941) p. 29.
 Grant, Heber J., Gospel Standards (1941) p. 30.
 Mormon 8:34, 35.
 Benson, Ezra Taft, A Witness and a Warning, Deseret Book, Salt Lake City, Utah, 1988, pp. 19, 20.
 Ether 3:14.
 D&C 20:9.
 D&C 17:6.
 1 Nephi 13:40.
 D&C 20:11.
 Galatians 3:24.
 Mosiah 13:30.
 Mosiah 13:27 – 32.
 Jacob 7:11.
 2 Nephi 25:26.
 Benson, Ezra Taft, A Witness and A Warning, Deseret Book, Salt Lake City, Utah, 1988, pp. 21, 22.
 Romney, Marion G., Ensign, May 1980, p. 67.
 D&C 84:85
 Benson, Ezra Taft, A Witness and A Warning, Deseret Book, Salt Lake City, Utah, 1988, p. 22.