The Bible testifies of the Book of Mormon, and the Book of Mormon testifies of the Bible. Mormon declared, “This [the Book of Mormon] is written for the intent that ye may believe that [the Bible]; and if ye believe that [the Bible] ye will believe this [the Book of Mormon] also” (Mormon 7:9).
President Brigham Young (1801–77) declared it impossible for someone who claimed to truly believe in the Bible to not believe in the Book of Mormon if they have seriously studied the Book of Mormon and learned its doctrines:
“No man can say that this book (laying his hand on the Bible) is true, is the word of the Lord, is the way, is the guide-board in the path, and a charter by which we may learn the will of God; and at the same time say, that the Book of Mormon is untrue; if he has had the privilege of reading it, or of hearing it read, and learning its doctrines. There is not that person on the face of the earth who has had the privilege of learning the Gospel of Jesus Christ from these two books, who can say that one is true, and the other is false” (Discourses of Brigham Young, sel. John A. Widtsoe [1954], 459).
One purpose of the Book of Mormon is to prove to the world that the Holy Bible is true (see D&C 20:11). By reading the Book of Mormon, a person’s testimony of the Bible increases. President Ezra Taft Benson (1899–1994) spoke of his love for the Bible and the Book of Mormon and how both testify that Jesus is the Christ:
“I love the Bible, both the Old and the New Testaments. It is a source of great truth. …
“… That sacred and holy book has been of inestimable worth to the children of men. In fact, it was a passage from the Bible that inspired the Prophet Joseph Smith to go to a grove of trees near his home and kneel in prayer. What followed was the glorious vision that commenced the restoration of the fulness of the gospel of Jesus Christ to the earth. That vision also began the process of bringing forth new scripture [the Book of Mormon] to stand shoulder to shoulder with the Bible in bearing witness to a wicked world that Jesus is the Christ and that God lives and loves His children and is still intimately involved in their salvation and exaltation” (in Conference Report, Oct. 1986, 100–101; or Ensign, Nov. 1986, 78).