Nephi's final statement of this discourse to his brothers answers an unasked question. While Nephi always refrains from pointing his sermons overtly at Laman and Lemuel, it is nevertheless clear that their rebelliousness is an undercurrent to the topics and approaches taken. Nephi makes this clear at the end of his sermon by addressing a specific justification of his brothers. They might tell themselves that they need not listen to Nephi or their father but Nephi assures them that these prophecies are found on the brass plates, a source even Laman and Lemuel must respect.
Literary analysis: While Nephi might complain of being weak in writing, he is clearly powerful in speaking (refer to 2 Nephi 33:1). Nephi's oral discourse is well crafted to nurse an argument. He presents his theme, and develops that theme with logic that is acceptable to his audience. He uses points on which they must agree to show them that they ought to agree with the central point he is making.
His craft in speaking is sufficient to work in the paralleling concepts to reiterate his message. Above all, he is uncompromising in his message, but not accusatory in his tone. While he may clearly be read as chastising Laman and Lemuel, it is not done overtly, and they will be chastened if and only if they are sufficiently repentant to hear, and to act upon their repentance. Otherwise, they might not even understand how clearly Nephi has pointed some of these sermons at them.