The literary purpose of these verses is to lead into the next section’s litany of Laman’s and Lemuel’s complaints. Nevertheless, it begins with a very plausible scenario. Nephi receives the command to make a ship, and by the time he could be observed making tools for the project, his brothers well understood that he was serious.
The situation is very human, and very understandable. Laman and Lemuel had a legitimate reason to suggest that “our brother is a fool, for he thinketh that he can build a ship.” This was a large task even if it were only to be a coast-hugging vessel. This was to be a ship that would cross the oceans into the complete unknown. Laman and Lemuel would have known enough of sailing to understand how difficult that was. They knew Nephi and knew his upbringing, so they knew he had never done anything like this before. They were reluctant to spend hard labor on a project that was doomed to failure.
In this incident, Nephi is showing another story that is similar to the return for the plates of brass. It is an impossible situation made possible only through God’s assistance. The brothers will eventually help, but only after they had seen that it was really going to happen.