The break between 1 Nephi and 2 Nephi has always seemed a bit awkward to me. Why break the text here? Nephi teaches his brothers at the end of 1 Nephi, but Lehi picks right up (in the same little meeting/gathering?) in 2 Nephi. I see lots of good reasons to break the 2 books apart from each other, but why here? (Why not after Lehi dies, for example?)
I think I may have one idea now. 1 Ne 19-22 is the last recorded speech of Nephi to his brothers. Does 1 Nephi’s end mark an end of Nephi as their teacher? Does 2 Nephi mark the beginning of Nephi’s role as king over the righteous, which only begins when Lehi dies? 2 Nephi recounts Lehi’s death, including last blessings, and then verses later Nephi is splitting off from the Lamanites and becoming a “king.”
One could read 1 Nephi as a fulfillment of 1 Nephi 2:22, and 2 Nephi as a fulfillment of 1 Ne 2:21,23-24.
1 Ne 2:22:
22 And inasmuch as thou shalt keep my commandments, thou shalt be made a ruler and a teacher over thy brethren.
1 Ne 2:21,23-4:
21 And inasmuch as thy brethren shall rebel against thee, they shall be cut off from the presence of the Lord.
23 For behold, in that day that they shall rebel against me, I will curse them even with a sore curse, and they shall have no power over thy seed except they shall rebel against me also.
24 And if it so be that they rebel against me, they shall be a scourge unto thy seed, to stir them up in the ways of remembrance.
So, the two books would be marked like this:
1 Ne: Nephi as younger brother, teacher, and prophet under Lehi
2 Ne: Nephi as king/prophet under no one else
Note that the heading for 2 Nephi, written by Nephi, says “Nephi’s brethren rebel against him” – not against Lehi or even the Lord, but against him. This wording suggests to me that now, beginning in 2 Nephi, he has become the ruler over the people (spiritually, at least). This also picks up on the language from 1 Ne 2:21 (“thy brethren shall rebel against thee“).
In 2 Nephi 1:28-9, Lehi seems to be giving Laman and Lemuel “one last chance,” which they promptly go against in 2 Ne 4:13. With this in mind, 2 Ne 4:13 and 2 Ne 5:1-5 seem to be the documentation that Laman and Lemuel have fully chosen to rebel against Nephi.
See also 2 Ne 5:19-20:
19 And behold, the words of the Lord had been fulfilled unto my brethren, which he spake concerning them, that I should be their ruler and their teacher. Wherefore, I had been their ruler and their teacher, according to the commandments of the Lord, until the time they sought to take away my life. (=1 Nephi)
20 Wherefore, the word of the Lord was fulfilled which he spake unto me, saying that: Inasmuch as they will not hearken unto thy words they shall be cut off from the presence of the Lord. And behold, they were cut off from his presence. (=2 Nephi)
I suppose you could see the 2 books as a documentation of the Lamanites, by looking at their decision to rebel first against Lehi (1 Nephi) and then against Nephi (2 Nephi).
Or rather, by dividing the two books here, it becomes more obviously history of the Nephite/Lamanite divide.
Though I could have made these arguments before, I always got hung up on the fact that the people don’t divide till 2 Ne 5. But I think it is helpful to see this in the context of Nephi’s promises in 1 Nephi 2, and that 2 Nephi starts when it does to show the fulfillment of 1 Ne 2:21,23-4 (and giving it a little bit of context.) 2 Nephi could actually be taken as its own book, without the stories of 1 Nephi, and the setting up of Nephi as king would still make some sense. Interesting. 1 Nephi as story of old-to-new world, 2 Nephi as story of life of righteous in new world. The list could go on and on … but it does answer some questions to me about what had seem to be an awkward place to switch to a new book.