"The Keystone of Our Religion"

The Book of Mormon: Another Testament of Jesus Christ is comparable to the Bible. It is, as the title indicates, another testimony of Christ and His mission here on the earth. It goes hand-in-hand with the Bible and teaches the fullness of the doctrine of Christ.
In the Bible, 2 Corinthians 13:1 we are taught that, "In the mouth of two or three witnesses shall every word be established." That counsel and reminder is given in The Book of Mormon as well in Ether 5:4 : "And in the mouth of three witnesses shall these things be established..."
God is a God of order. There is no chaos in His work. Because He has said that two or three witnesses will establish His word, He will follow that law. The Book of Mormon is that second witness.
In the Introduction of The Book of Mormon it states that, "...The Book of Mormon [is]...the keystone of our religion..." The keystone of an arch is what allows is to remain upright.

Without a keystone, the arch would fall in on itself. Likewise with The Book of Mormon. If this book of not true, then The Church of Jesus Christ of Latter-Day Saints is not. However, if The Book of Mormon is true then The Church of Jesus Christ of Latter-Day Saints is Christ's church once again established and restored to the earth in these days.
I know that The Book of Mormon is God's word. It is a second witness to the divinity of Christ as the Son of God. The Church of Jesus Christ of Latter-Day Saints is Christ's church on the earth today. It is the only true church. I know that because I have been taught it by the Holy Ghost.
The last two paragraphs in the Introduction of The Book of Mormon say, "We invite all men everywhere to read the Book of Mormon, to ponder in their hearts the message it contains, and then to ask God, the Eternal Father, in the name of Christ if the book is true. Those who pursue this course and ask in faith will gain a testimony of its truth and divinity by the power of the Holy Ghost. (See Moroni 10:3–5.)
 Those who gain this divine witness from the Holy Spirit will also come to know by the same power that Jesus Christ is the Savior of the world, that Joseph Smith is His revelator and prophet in these last days, and that The Church of Jesus Christ of Latter-day Saints is the Lord’s kingdom once again established on the earth, preparatory to the Second Coming of the Messiah."
I know that the Book of Mormon is the word of God and you can come to know that for yourself. If you will read, think about and ponder, and pray to know of its truthfulness, the Holy Spirit will manifest the truth to you. That is a promise.