1 Nephi 13

Nephi records of his vision -

"...that I beheld the remnant of the seed of my brethren, and also the book of the Lamb of God, which had proceeded forth from the mouth of the Jew, that it came forth from the Gentiles unto the remnant of the seed of my brethren." (Book of Mormon | 1 Nephi 13:38)

Seeing that the seed of Lehi had received the Bible, then -

"...after it had come forth unto them I beheld other books, which came forth by the power of the Lamb, from the Gentiles unto them, unto the convincing of the Gentiles and the remnant of the seed of my brethren, and also the Jews who were scattered upon all the face of the earth, that the records of the prophets and of the twelve apostles of the Lamb are true."
(Book of Mormon | 1 Nephi 13:39)

It become evident that the Book of Mormon as well as modern revelation are not only another testament of Jesus Christ but also that the Bible is true. Many Christians of our day, believe the Bible to be true because they have been told so. But with these "other books", we have further testimony of the truthfulness of the Bible. And not only that the Bible is true, but also these "other books" -

"...shall establish the truth of the first, which are of the twelve apostles of the Lamb, and shall make known the plain and precious things which have been taken away from them; and shall make known to all kindreds, tongues, and people, that the Lamb of God is the Son of the Eternal Father, and the Savior of the world; and that all men must come unto him, or they cannot be saved." (Book of Mormon | 1 Nephi 13:40)

What Christian would not want access to these truths for these other books shall -

"...come forth unto the Gentiles, by the gift and power of the Lamb.
36 And in them shall be written my gospel, saith the Lamb, and my rock and my salvation.
37 And blessed are they who shall seek to bring forth my Zion at that day, for they shall have the gift and the power of the Holy Ghost; and if they endure unto the end they shall be lifted up at the last day, and shall be saved in the everlasting kingdom of the Lamb; and whoso shall publish peace, yea, tidings of great joy, how beautiful upon the mountains shall they be." (Book of Mormon | 1 Nephi 13:35 - 37)