According to John Tvedtnes, an author may promise in the course of writing to return to a subject later to supply further details. Actually keeping such a promise can prove difficult. Even with modern writing aids, memory can betray a person into failing to tuck in the corners of plot or information. Mormon, the editor of much of the Book of Mormon as we have it, made these types of promises at least seven times. In each case, he or his son Moroni followed through perfectly.
Mormon speaks in Mosiah 21:35 of Limhi's people, saying that "an account of their baptism shall be given hereafter." Almost a hundred verses follow before he recounts the performance of that ordinance (see Mosiah 25:17-18). [John A. Tvedtnes, "Mormon's Editorial Promises," in Rediscovering the Book of Mormon, p. 29]