Textual: Mormon does a very curious thing at this point. He stops quoting and begins summarizing.
We can only guess as to Mormon’s reasons for stopping this discourse, because he has copied much longer texts before (such as Abinadi before the priests). Perhaps Mormon felt that this got the point across, and more was not essential.
If we remember that Mormon is much more interested in the faith of the people, it may be that this text is included because it was clearly important, but having been sufficiently explained, no longer became important to Mormon’s main thesis. We simply cannot tell. Mormon hasn’t left enough clues to this particular puzzle.