When Nephi comes to his father’s tent, his father has had another dream. In this dream, Lehi is commanded to have his sons return to Jerusalem to retrieve the plates of brass. This will be a long story, and Nephi will use that story to emphasize the ways in which he is becoming the ruler and teacher over his brothers, as Jehovah prophesied.
The command to retrieve the plates of brass begins with the emphasis that they contain the genealogy of Lehi’s forefathers. After the brothers return with the plates of brass, Nephi will record (in 1 Nephi 5:14) that Lehi does learn of his genealogy, a genealogy which ties him to Joseph of Egypt.
For Nephi, this was an important aspect of the story of the plates of brass. The plates of brass will be kept with Nephi’s people. For that new people, the genealogy traces the antiquity of Nephi’s claim to rulership. As a descendant of an illustrious ruler, substance was given to Nephi’s New World claim to rulership. When this record was written, those were important concerns.
The final two verses continue the theme which contrasts Laman and Lemuel with Nephi. It is a contrast that Lehi had already acknowledged when he prayed that Laman be like the river and Lemuel as the valley. In this case, Laman and Lemuel murmur (again recalling the rebellious Israelites as Moses led them in the wilderness). Nephi is favored of Jehovah, because he has not murmured.