I once heard Elder Jeffrey R. Holland say that, if you could keep only one chapter in the Book of Mormon, 2 Nephi 2 would be the chapter to choose. It explains moral agency and shows it in its central role, connecting it to the fall and the atonement. Agency is the power inherent in all human souls to choose between good and evil, knowing which is which, and understanding that moral choices come with consequences.
Here Lehi also teaches something most of the religious world does not yet understand: The fall of Adam and Eve was no accident or surprise. It was part of God’s plan. Its ultimate results, because of the atonement, are life and joy: “Adam fell that men might be, and men are that they might have joy. And the Messiah cometh in the fulness of time, that he may redeem the children of men from the fall. And because that they are redeemed . . . they have become free forever, knowing good from evil. . . . And they are free to choose liberty and eternal life . . . or to choose captivity and death” (2 Nephi 2:25-27).