Most people who've been to been to Latter-day Saint seminary know the mildly interesting acronym spelled by a few words in 2 Nephi 9:39: "[To be] spiritually-minded is life eternal," or SMILE.
For the fun of it, I decided to see what other acronyms there were in the Book of Mormon. Following are a sampling (not all the phrases that make up the acronym make sense; I just chose a few of the more interesting/amusing acronyms):
PALATES: "perish as long as the earth should" (tied for longest)
HANDOUT: "hearts are not drawn out unto the" (tied for longest)
WOMBAT: "words of my beloved are true"
SITCOM: "strong in the city of moroni"
TWEETS: "the whole earth except they shall"
MAIMS: "mine account i must speak"
SCUMS: "son came unto me saying"
WITCH: "which is to come having"
PANIC: "peace and now it came"
NACHO: "naught and cast him out"
ALOHA: "and lowliness of heart and"
All in all, I found over 400 that were 5 letters or longer, although some were duplicates.