According to Hugh Nibley, when Nephi says, "that I may be strict in the plain road" (2 Nephi 4:32) he means "that I may stick to the right path." At the end of the first Psalm it says, "The way of the wicked shall be lost in the sand." That is, Nephi doesn't want to get lost in sin. The "path of the low valley" is the easiest path to take and the surest, not having to run up and down any hills or anything like that. [Hugh W. Nibley, Teachings of the Book of Mormon, p. 251]