As with many other cases where a testificatory Amen occasioned the close of a chapter, the beginning verses of this next chapter finish the story of the previous chapter. That chapter centered on the story of the Ammonites, and Mormon needs to conclude those events.
Even though the immediate story of the Ammonites has ended, this will not be the end of their importance to the overall Nephite story. They are established in Jershon and protected, but this original 1830 chapter (which covers the modern chapters 30–35) will set up conditions that will directly threaten Jershon. In keeping with the message of Alma’s soliloquy in Alma 29, even though there will be temporal causes and reasons for the threat to Jershon, it will ultimately be a spiritual threat.
The original 1830 chapter deals with Nephite apostasy. We will get two stories: the first of Korihor and the second of the Zoramites. In both cases, Mormon will continue to underline his theme that the most dangerous enemies are those who were once Nephites.