There is minor disagreement among scholars as to the identity of the “beloved” disciple of Christ. Read this Wikipedia entry for a summary: http://en.wikipedia.org/wiki/Disciple_whom_Jesus_loved. It is postulated that the beloved disciple is John, Lazarus, Mary Magdelene, or someone else. While there is weak to no evidence for the beloved disciple to be anyone other than John, discussion still continues (even though it should never have started).
In the Book of Mormon we have a record of Jesus speaking to three of His Nephite disciples who desired to remain and preach the gospel until Christ’s return: “And he [Jesus] said unto them: Behold, I know your thoughts, and ye have desired the thing which John, my beloved, who was with me in my ministry, before that I was lifted up by the Jews, desired of me.” (3 Ne. 28:6).
Instant clarity. End of discussion.
I use this as an example of the role of the Book of Mormon. It clarifies much of what appears controversial or unclear in the Bible. The Book of Mormon serves as another witness of Jesus Christ and of the Bible. It establishes the truth of the Bible so that we may more fully believe it and believe Christ.