Nephi again notes that he has not taught his people the understanding of Isaiah, and then very specifically declares that as one who lived in Jerusalem, Nephi has two qualifications. The first has already been stated, and is merely implicit in the restatement of Nephi’s time in Jerusalem - contrasted with his conscious decision not to teach the manner of prophesying to his people. It is not that Nephi does not himself know, and therefore doesn’t teach, but rather that he does know, and declines to teach. His inherent Old World knowledge is made explicit in his experience in Jerusalem and the “ regions round about” which gave him personal knowledge of the fulfillment of some of Isaiah’ words.
The fulfillment Nephi refers to is the captivity by Babylon, of which his father preached, and for which preaching the family left Jerusalem. The experience in the “lands round about” must refer to the time after the departure from Jerusalem, for any direct evidence Nephi would have had of the destruction of Jerusalem would have come from the accounts passed on in these other lands, even though he also could claim confirmation through revelation .
Having established his authoritativeness, using the destruction of Jerusalem as firm case in point, Nephi declares that he will not discuss that destruction. That is past, and impacts his future generations only in the circumstances of their location. Nephi’s concern is with the prophetic utterances of Isaiah that he sees as pertaining to yet future generations. It is to these people, and these issues, that Nephi will turn in discourse.
Narrative: Verse 6 is a restatement of the theme of verses 1 and 2. Presuming that verses 1 and 2 were his intended transitional material, the return to that transitional material suggests that Nephi recognized his divergence from his purpose, and now resumes his original intent.