The answer to your question is found in the Book of Mormon itself.
What is the purpose of the Book of Mormon? Read its title page and D&C 20:1–12.
How do you explain simply to someone what the Book of Mormon is? Read the introduction to the Book of Mormon.
In the New Testament, the Apostle Paul taught, “In the mouth of two or three witnesses shall every word be established” (2 Corinthians 13:1). The Book of Mormon does just that: it is another witness of Jesus Christ, establishing His word, His gospel.
For more help on this question, see Preach My Gospel (2004), chapter 5, and True to the Faith (2004), pages 157–58.
I would tell your friends that the Book of Mormon is a sacred record of the ancient inhabitants of the Americas. Like the Bible, it testifies of Jesus Christ. However, it clarifies doctrines taught in the Bible. It is a book of scripture brought to light in these times by God’s power to help a dark world come to know Jesus Christ.
Ashley B., 18, Colorado
The Book of Mormon is a lot like the Bible. It talks about prophets who communicated with God to lead His people, just like Moses led the children of Israel. And after Christ ascended into heaven, He visited the people in the Americas and performed miracles, just like He did in the New Testament.
Matthew T., 15, Virginia
I would just tell them the truth about the Book of Mormon and how it came to be. You don’t have to explain to them all the details, but you could challenge them to prayerfully read a bit of it.
Tanner M., 16, Utah
Tell them that the Book of Mormon is a second witness and testament of Jesus Christ as our Lord and Savior. It is not meant to replace the Bible but to enhance our understanding of the doctrines presented in it. The Book of Mormon was written by ancient prophets for us, in our time, to strengthen us. It is an account and a witness that following His Resurrection, Jesus Christ visited and ministered in the Americas as well as in Jerusalem. This fortifies the truth that the gospel of Jesus Christ is for everyone, everywhere.
Amelia H., 18, Ohio
You can refer your friends to John 10:16. This scripture is talking about the people in the ancient Americas and how Jesus Christ will teach them too. You could refer them to its cross-reference in the Book of Mormon, 3 Nephi 15:21.
Breann P., 16, Utah
It’s great that your friends already believe in the Bible. You’re already over the first hurdle. Now, to get over the second, explain that Jesus Christ speaks to all His children, not just those in Jerusalem, and that the Book of Mormon contains His teachings to those in the Americas. Explain that the Book of Mormon isn’t a new Bible but teachings from Jesus Christ so we can learn more.
Katie N., 16, England
I think the best answer is in the introduction to the Book of Mormon. It begins: “The Book of Mormon is a volume of holy scripture comparable to the Bible. It is a record of God’s dealings with the ancient inhabitants of the Americas and contains, as does the Bible, the fulness of the everlasting gospel.” The Bible is a record of God’s dealings with the ancient inhabitants of the Old World. The Book of Mormon is a record of God’s dealings with the ancient inhabitants of the Americas, but they are very similar. You can also quote article of faith number eight.
Astraya J., 13, Utah