It is significant that the Savior calls out Nephi. Nephi had been a powerful prophet, and there would be no one else that would merit the position of such divine and public recognition. When the Savior would later designate his disciples (the Book of Mormon term for what we would call apostles), it is certain that Nephi would be the head of that body, and therefore head of the church. It is also probable that this Nephi later became the head of the new Nephite nation, and therefore it is for him that our book of 4 Nephi would be named.
Starting at this point, and through the end of the chapter, the instructions are given to the twelve rather than to all who had gathered. Those gathered undoubtedly heard the instructions, but the teachings were directed to the twelve. The shift from speaking to the congregation and then to the twelve, and then to the congregation, will occur again during Christ’s visit.