This letter is a stark contrast to the letter in Chapter 8. That letter was more formal, almost what we might call a First Presidency letter. This is clearly a letter from father to son, and it passes on the information of the day: sad information, but needed information.
Even though Mormon and Moroni are far enough apart that they have to resort to letters, and Mormon is clearly on the frontlines of the war, Moroni would have heard of the conflicts even though they had not yet reached where he was at the time. Therefore, it is most appropriate for his father to note immediately, that “I am yet alive.”
In Moroni 8:4, Mormon wrote of something that “grieveth [him] exceedingly.” Now he writes of very different news, “which is grievous.” These are hard times.
Mormon tells Moroni that the war is not going well. They are losing important men, or at least men that Moroni would have known, and for whom he would grieve. Most importantly, however, is that Mormon “fear[s] lest the Lamanites shall destroy this people; for they do not repent.”
That is an interesting statement because it is not only a prediction throughout the Book of Mormon, but a theme that Mormon ties to the destruction of the Jaredites. Yet, at the time of this letter, it might appear that Mormon does not yet know, but only fears, that the destruction will come.
The details of the timing of this letter are beyond these notes, but it appears highly likely that the Book of Mormon was written after this letter. Hence, we are seeing a time prior to the writing of Mormon’s masterwork, a time when perhaps he held out just a little hope; a time when he at least feared their destruction rather than knew it too well.