One of the important functions of 1 Nephi is to show how the promise that Nephi would be a leader and a teacher over his brothers would play out. This is important because it is contrary to expectations, as the eldest child traditionally fills that role. However, the Bible has a number of such stories, which carry the subtext that Jehovah is behind these events precisely because they are an alteration of the expected order.
As Nephi begins this part of his story, he has just finished his vision of what his father saw. His brothers not only did not have such an experience, but Nephi finds them disputing what their father had said prior to the time that Nephi entered his vision. This return to the time right after his father’s explanation of the Savior emphasizes the contrast between his brothers and himself. They are still stuck in the past questions while Nephi has just come from a transcendent experience of which they not only did not take part, but of which they are totally ignorant.
Nephi’s vision of the future now sees this conflict with his brothers in its prophetic perspective. They dispute now because of the hardness of their hearts, and Nephi has seen that their hardness of hearts will continue, and will define the relationship between their descendants and Nephi’s descendants.