I want to start by posting a portion of a response I wrote for my LDS message board. It's not the best writing I've done, but it conveys the spirit of this blog.
I've been long pondering something about this. You see, missionaries often claim that the Book of Mormon serves as witness to the truthfulness of the Bible and both testify of Christ. So far so good. Christianity is splintered because they don't have that second testament. Um, wait.
On my mission, I remember a man on the street asking my companion and me, "If the Book of Mormon is supposed to cut through the confusion, then why are there so many Mormon factions?" He had a good point.
I decided that that line of reasoning might work for a new investigator, but there has to be more. The church isn't true just because the Book of Mormon exists, or the RLDS church and all the others would also be true. No, it is the principle of continuing revelation that makes a church true. It is the unbroken authority that makes a church true. The Book of Mormon helps, but is not the only thing. It is the Holy Ghost that confirms which is true. You can't just use the Book of Mormon, because it is not enough. Neither is the Doctrine and Covenants (or Book of Commandments). Again, it is the Holy Ghost that will tell you the truth of all things.