Brant Gardner notes in Alma 37:23 that Alma is citing a text that is no longer extant. It must be an old text because it is describing the creation of the interpreters that eventually find their way into Alma's hands. The Lord provided the stone (here in the singular, elsewhere specifically two stones, such as Ether 3:23) in order to "shine forth in darkness unto light." [Brant Gardner, Book of Mormon Commentary, [http://www.highfiber.com/~nahualli/LDStopics/Alma/Alma37.htm], p. 9]