Textual: When Nephi enters a new topic into his text on the plates, he is very consistent in providing a transition from the previous material to the new material. Most recently, chapter 31 begins with a written transition that links the previous text to the recorded speech which follows. Likewise here, we have a transitional text.
It is significant in this transitional introduction that Nephi specifically contrasts speaking and writing. We might suppose that this is a generic lament, but it is very clearly part of the transition, and as such, is intended to provide a linkage between what has just been recorded and what will follow. Thus the transition from speaking to writing is the final confirmation that Nephi has been recorded an oral discourse. Nephi is making a distinction between the oral discourse mode and the time when he must write directly on the plates (a process of sufficient cumbersome nature that it would have been more difficult for him to rapidly respond to the promptings of the spirit - and as any good speaker understands, the spiritual interaction of the audience that can prompt excellence through the Spirit).
This is also a transition because he moves from a speech about the power of the Spirit to a written testimony that he wants the Spirit to confirm. Nephi’s expectation is that such confirmation occurs freely in the oral context, but he is less sure of its efficaciousness in the written context - Nephi will not be around to convey his personal spiritual power to the future reader as he can in oral discourse to a contemporary audience.
The final aspect of this transition is the movement from a direct discourse to a contemporary audience to a testimony directed at future populations. Where the previous chapters specifically supplied information to his own people, this chapter is specifically addressed to the future. Thus we have a dramatic shift that is occasioned not only by the chapter division, but in the nature of this chapter from the previous two.
Speculation: Why this abrupt end to the previous discourse, and now this final chapter? There are three important pieces of information:
At the time Jacob makes the above statement it is fifty five years after the departure of Lehi from Jerusalem (Jacob 1:1). Therefore, Nephi is probably less than 75 years old, and certainly older than 65. Even the younger of these two ages places him on the extremes of ancient life expectancy. What is significant is that Nephi understood enough of his impending death to be able to organize his affairs. This precognition of his time is the probable explanation for the abrupt ending of the discourse.
We may speculate that Nephi had been writing the discourse, and left off for some reason - expecting the departure from writing to be temporary. We must remember that the discourse itself was given earlier and then written later, so the discourse when given would have had the ending we are missing. In between the time he leaves writing the discourse and the beginning of chapter 33 he accedes to the knowledge of his short time, and rather than return to the discourse, turns to a final testimony so that he may hand the plates over to Jacob and complete the orderly exchange of affairs.
This exchange of affairs includes the handing of the small plates over to Jacob - a recorded fact. What is not recorded is the likely greater necessity of handing over the governance of the city. This would have included the large plates as well as any other tokens of rulership (including the brass plates, the Liahona, and the sword of Laban). We don’t have this information because it would have been recorded in the large plates, which we do not have for this period.
In this scenario it is tempting to suppose that Nephi ended where he did in chapter 32 because he was not feeling well, and when he felt well enough to write again, did so only to place a formal close to his record, much as he began it formally in 1 Nephi 1.