Although Nephi begins a new book, he picks up where he left off. His introduction is that he concluded speaking to his brothers. Immediately, he has Lehi speaking to them. This suggests that Nephi began writing the book of 2 Nephi soon after ending 1 Nephi. As noted in Episode 186, Nephi is telling a story of two worlds, and tells his people’s origin story from the perspective of each of those worlds.
In each of the two stories, the genesis of the Nephite people is placed in the hands of Lehi’s prophecies. In the Old World he preached repentance to the people of Jerusalem, and said that elsewise, they would be destroyed. In the New World, his descendants must repent, else they will be destroyed.
There is another subtle shift in the way Nephi is telling the story. This is where the information in the header helps us understand Nephi’s thought process. He had created the first book to discuss the exodus from Jerusalem and the events that led them to the New World. In that book, he set the stage for how he was the prophesied teacher over his brothers, but there was still the prophesy of him becoming a ruler. That was to happen in the New World.
Thus, 1 Nephi was the Old World and the development of the teacher, and 2 Nephi was for the New World and the development of the ruler. This book was to cover the essential formation of the Nephites in the New World. After Lehi’s family arrived in the New World, they continued as a family. They would later divide into what will become Nephites and Lamanites. Lehi’s prophecies and blessings to his sons set the stage for the division into Nephites and Lamanites.