The Book of Mormon is an essential part of our belief. Listed below are some reasons why.
WHAT IT IS ...
In John 10:16, Jesus says, "And other sheep I have, which are not of this fold". The Book of Mormon is a record of His ministry to these "other sheep". Just as the Bible is a collection of Divinely Inspired writings by disciples of Jesus in Jerusalem and areas round about, the Book of Mormon is a collection of Divinely Inspired writings by disciples of Jesus, these "other sheep".
WHAT IT IS NOT ...
IT IS NOT ANOTHER BIBLE
In fact, The Book of Mormon states that the Bible and The Book of Mormon go hand-in-hand testifying to the Divinity of Jesus.
IT IS NOT ANOTHER BIBLE
In fact, the Book of Mormon writers only cover the time period after the dispersion at the Tower of Babel. They carried the Old Testament portion with them and quoted from it frequently.
IT IS NOT ANOTHER BIBLE
It is neither more important, nor less important than the Bible. They are equally important to understanding Christ's message, especially the restoration of the House of Israel.