Historical information: As Jacob begins this speech he makes it clear that this is not the first address to his brethren the Nephites. Certainly Nephi had never stopped caring for and preaching to his people, but it is equally obvious that Jacob took an active role in the preaching and teaching of the gospel during Nephi's lifetime (obvious because Nephi is writing this sermon given by Jacob).
Once again there is an implication here of a population larger than the more logical 20-25 people that might have been expected from the Lamanite-Nephite division. It is also significant from the standpoint of defining social order, that there is no preclusion of Jacob from preaching. Therefore not all of the political and religious functions are exclusively centered in Nephi.
It is possible, and possible only if there were a larger population, that there is the beginnings of a political/religious division of responsibility. The political responsibilities rest with Nephi, and Jacob takes the more spiritual approach. This possibility is pushed to probability by the evidence of the transmission lines of the two sets of plates Nephi created.
Very clearly, the small plates remain with Jacob, as Jacob is the next writer on them. Positing a political/religious division at the time of Nephi, the small plates are handed to Jacob where they continue in his direct line. As for the small plates, this is made explicit as Jacob begins to write:
1 For behold, it came to pass that fifty and five years had passed away from the time that Lehi left Jerusalem; wherefore, Nephi gave me, Jacob, a commandment concerning the small plates, upon which these things are engraven.
Jacob 1:2
2 And he gave me, Jacob, a commandment that I should write upon these plates a few of the things which I considered to be most precious; that I should not touch, save it were lightly, concerning the history of this people which are called the people of Nephi.
Jacob 1:3
3 For he said that the history of his people should be engraven upon his other plates, and that I should preserve these plates and hand them down unto my seed, from generation to generation.
Jacob was the religious leader, but clearly not the next political leader:
9 Now Nephi began to be old, and he saw that he must soon die; wherefore, he anointed a man to be a king and a ruler over his people now, according to the reigns of the kings.
Had that man been Jacob, certainly we would have known that. Thus Jacob is a religious leader, and the explicit keeper of the small plates, and this unnamed man is the political leader. The large plates stay with the political tradition.
Once again, however, this is a clear indication that the population was sufficiently large when Nephi died that there could be an explicit division between the religious and the political. It is also interesting that in a lineage history, that the name of the next ruler is not given. In fact, the succession of kings - a topic that must surely have been significant on the large plates, is virtually absent in Jacob. The clearest indication is that there is a significant division, and that the political lines did not follow Jacob's descendants. While we cannot be certain, there is at least an intriguing possibility that the political line might not have followed Nephi, though one would expect it should. For whatever reason, the names of the kings are absent from Jacob's record.