The twenty-four plates refer to the record of Ether that was discovered by the people of Limhi (Mosiah 8:7-9). While Mosiah gave a translation, it was not included in the record at that time, and we will not see it until Moroni adds it at the end of this volume. Alma tells Helaman that there is dangerous information contained therein, but that it is important that they record be retained. The purpose for keeping the book of Ether, according to Alma, is to destroy secret works of darkness. When Moroni adds the book of Ether to his father’s record, he does emphasize the role of the works of darkness in the destruction of the Jaredites, and therefore fulfills this part of the stated purpose for the plates.
We also learn that along with the plates were given the interpreters. We have seen these interpreters before in connection with the 24 plates. They were used by Mosiah to translate. What we will now learn, is the history of those interpreters among the Jaredites. For more information on the transmission path of the interpreters from the Jaredites to Mosiah, see the commentary following Mosiah 8:13.
Textual: While the current context concerning the interpreters is a transition from this mention to the discussion that follows, it is interesting that when Alma discusses the preservation of the plates of Ether, he also discusses the interpreters. We have two things that we must track concerning the record of Ether. There is the original twenty four plates, and there is the translation made by Mosiah. When Moroni gives us an abridgement of the record of Ether, there is no indication that he is translating the original plates by means of the interpreters. He appears to be using the translation made by Mosiah.
Nevertheless, Alma is telling Helaman that the plates must be preserved. It would appear that there is an understanding of the separation between the translation and the original, and the admonition to Helaman concerns the original plates, hence the need to include the interpreters. Because Mosiah’s text had already been translated, one would not need the interpreters to read it. Those are important only to a future new translation. There is no indication in the Book of Mormon as we have it that those original plates were ever translated again. This instruction to keep the original plates may have been something akin to keeping the original evidence, in case it was needed to corroborate the translation.