1 Nephi 16:9–10
9 And it came to pass that the voice of the Lord spake unto my father by night, and commanded him that on the morrow he should take his journey into the wilderness.
10 And it came to pass that as my father arose in the morning, and went forth to the tent door, to his great astonishment he beheld upon the ground a round ball of curious workmanship; and it was of fine brass. And within the ball were two spindles; and the one pointed the way whither we should go into the wilderness.
“Like the Urim and Thummim, the Liahona was a physical device that aided in the coming forth of revelation. Mechanically, it pointed the direction of travel for Lehi’s family (see 1 Nephi 16:10). The Liahona, however, had more than a mechanical function. The arrows or pointers only worked according to faith (see v. 28). Even more remarkable, on the ball appeared writing which instructed and exhorted Lehi’s family (see vv. 26–27, 29). Nephi indicated that the writings were ‘plain to be read’ and gave ‘understanding concerning the ways of the Lord’ (v. 29).
“The Liahona was indeed a remarkable instrument. In it Alma saw a type or symbol of the word of God, or the gospel (see Alma 37:38–47). The Liahona was treasured by the writers of the Book of Mormon and seems to have been passed on with the plates. It, along with the plates, the Urim and Thummim, the breastplate, and the sword of Laban were shown to the Three Witnesses by Moroni (see D&C 17:1).”
(Book of Mormon Student Manual, rev. ed. [Church Educational System manual, 1996], 16.)