Nephi provides the ultimate condemnation of Laman and Lemuel. Just as did those in Jerusalem, they sought Lehi’s life. Nephi gives us no more information than this. Apparently, Lehi spoke to them in the power of the Spirit at a time sufficient to prevent their attempted patricide. The description of them shaking before Lehi as the result of the power of the Spirit will be reprised when Nephi must employ the same power of the Spirit to thwart their murderous attempts, but at that time against Nephi rather than Lehi. Nephi wants his readers to remember this incident when they read the later one, because it is one of the ways that Nephi begins to show that he is the rightful heir of his father’s prophetic mantle, and his father’s role as the leader of the extended family.
There is also a literary function in tying Laman and Lemuel to those in Jerusalem. Lehi called those in Jerusalem to repentance, else Jerusalem would be destroyed. When Nephi specifically notes that Laman and Lemuel do not believe that Jerusalem could be destroyed, he defines their ideology as that of the Jerusalem against which Lehi preached. Nephi has Laman and Lemuel carry that disbelief and distrust in God’s message and messengers across the ocean, where it will define the relationship between Lamanites and Nephites.
Verse fifteen is a seeming anomaly. We know that it is not, because Nephi will use that statement, or something similar, more times during his record. In this case (as in most others), it marks a shift in the narrative. One story ends, and another will begin.