The Book of Mormon contains the fulness of the gospel of...

The Book of Mormon contains the fulness of the gospel of Jesus Christ (D&C 20:9). That does not mean it contains every teaching, every doctrine ever revealed. Rather, it means that in the Book of Mormon we will find the fulness of those doctrines required for our salvation. And they are taught plainly and simply so that even children can learn the ways of salvation and exaltation.