Mormon began this discussion of his writing by noting that he couldn’t write the hundredth part of what the plates of Nephi contained. At the end of the insertion, he notes that he wanted to write more, but the Lord constrained him. It is important to note that Mormon said: “And now I, Mormon, make an end of my sayings, and proceed to write the things which have been commanded me.” There were things he was commanded to write, in addition to those things that he was not to write.
When he says that he makes an end of his sayings, he is declaring that the insertion of his own thoughts as the editor or historian are ended, and he is returning to his role as the narrator of events.