My mother recently finished reading the Book of Mormon. Again.
She remarked in her family email today, "I really do see something new every time I read it." This is a common claim in Mormon culture (one that I thought my mother was better than) that really, really gets under my skin. I've heard many people bear their testimonies about the truthfulness of the Book of Mormon based on the idea that they learn something new each time they read the book. I guess there's a simple fact that these people have overlooked: The Book of Mormon is long.
The Book of Mormon has more than a quarter of a million words. Unless you have an eidetic memory, if you don't notice some nuance of meaning that didn't occur to you the last time you read it (or that did occur to you, but slipped your mind over the last 200,000 words), then you're just not paying attention.
You don't hear me bearing my testimony of the truthfulness of Stephen Crane just because I noticed another clever use of color to evoke unexpected imagery the last time I read The Red Badge of Courage. I don't believe that George Orwell has done more for mankind than anyone except Jesus Christ despite the fact that I uncovered a profound truth of human nature last time I perused Nineteen Eighty-Four. Nor do I mourn Michael Crichton as a departed prophet because I didn't realize, upon my first reading, that he used the remote, underwater setting of Sphere to explore a theme of isolation. (Although Crichton might have to be a fallen prophet, considering how he liked to screw his books up when he made them into screenplays.)
Great poetry can be only a few lines but open itself up to many interpretations and multiple relevant layers of meaning when it's read carefully and repeatedly. This trait is not unique to the Book of Mormon in any way.
And, to be honest, the Book of Mormon is far from the greatest example of this trait anyway. That's what we have literature for.