Redaction: When Mormon says that he writes “again,” he confirms the existence of other letters. While it is possible that this statement refers to the letter included as Moroni 8, it seems more likely to me that Moroni selected two of several letters to copy than that Mormon wrote only two to his son. We cannot even be sure that Mormon wrote this letter at some point after writing the first letter. Moroni could just as easily have received this letter before the one he quoted in chapter 8.
The letter’s subject does, however, seem to come from a later period. The military situation Mormon describes at the end of chapter 8 has worsened, suggesting a later point. The letter in chapter 8 dealt with a point of doctrine that was at least tangentially related to the earlier liturgical chapters; but this chapter is neither liturgical nor doctrinal. It is purely historical. The only connection, if one genuinely exists, is to the theme of repentance Mormon mentioned in his letter’s close. The mere association of ideas seems to be Moroni’s reason for including it, again suggesting that he is working without a guiding outline. His decision to include this letter is not dictated by his book’s overarching purpose but rather because of a topic that came up almost as an afterthought in the end of the letter. His focus is not on the whole, but on the particular instance.
Chronology: H. Donl Peterson suggests:
Mormon expressed hope that he would soon see Moroni, since he had the sacred records that he desired to transmit to Moroni. This writer dates this epistle about 384, since Mormon had finished the abridgment that would be entrusted to Moroni’s care and the gathering for the final battle was not yet completed. When Mormon said he hoped to see Moroni soon it appears that the word had gone out for all the remaining Nephites to rally to the land of Cumorah for the final battle.
Peterson’s A.D. 384 would be approximately 375 in the correlation I am using. This is a time period just before the final battle at Cumorah. (See commentary accompanying Mormon 6:5.) Certainly this letter was written prior to that time, as Mormon and Moroni were together at that point and writing was unnecessary.