Nephi speaks with conviction buttressed by personal revelation, prophesying Laman’s and Lemuel’s fate should they return to Jerusalem. The reaction of Laman and Lemuel (and that of their future wives) makes it clear that, while they understood the words, they rejected his inspiration.
Vocabulary: “And now, if ye have choice, go up to the land.” Skousen suggests:
The reader might be confused over the meaning of “if ye have choice.” It doesn’t seem reasonable to interpret the subordinate clause literally. Nephi isn’t really asking whether Laman and Lemuel and the others have a choice. They apparently have their agency and could return if they wanted to. One possible way to interpret the conditional clause would be to replace the if with since (“and now since ye have choice / go up to the land”). A more plausible equivalence in modern English would be to replace have choice with the verb choose: “and now if you choose / go up to the land.” In other words, the meaning is something like “and now if you wish / go up to the land.”