So many where do I start! The title of the Book of Mormon says Another Testament of Jesus Christ. In the Bible we have the Old Testament, which is a record of all of God's prophets and dealings with his people before Christ. It also contains the New Testament, which is a record of Jesus Christ and his mortal ministry. With the Book of Mormon being Another Testament, its purpose isn't to take away from the Bible, but to ad on to the truths of the Bible.
The Book of Mormon is saturated with the Holy Ghost. It is impossible to read the book with faith and with a real determination to know of the teachings and not feel the Holy Ghost. I like what the Prophet Nephi says, "And if ye shall believe in Christ ye will believe in these words, for they are the words of Christ, ... and they teach all men that they should do good." (2 Nephi 33:10) As we read the Book of Mormon, the words teach us all that we must do good. Living by the principles taught will bless the lives of those who decide to follow and abide by them faithfully.
question, What is the Purpose in the Bible? The Bible has many purposes, but the gospel writer and Apostle John tells us specifically what its purpose is. He says "And many other signs truly did Jesus in the presence of his disciples, which are not written in this book: But These are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name." (John 20:30-31)
Now let's turn to the Book of Mormon to see what its purpose is. The Prophet Mormon tells us what the Purpose of the Book of Mormon is. "And behold, they shall go unto the unbelieving of the Jews; and for this intent shall they go-that they may be persuaded that Jesus is the Christ, the Son of the living God." (Mormon 5:14)
They are worded almost exactly the same, and I know that the purposes of both records are to bring people closer to Christ. The only way one can know for themselves what the purpose of the Book of Mormon is, is to just read it. A new light will come into your life if you do so, and you will be able to know that these really are Christ's words. http://www.mormon.org/book-of-mormon/