Nephi identifies his future audience as descendants of Israel. He asserts that Isaiah is relevant both to Old World Israel (Isaiah’s audience) and to New World Israel (Nephi’s). Because Isaiah’s message will be obscure to anyone lacking the spirit of prophecy, Nephi, speaking prophetically, will expand on some of Isaiah’s themes to underline and support his own vision. However, unlike Isaiah (and Lehi), Nephi prophesies in “plainness,” thus consciously eschewing the Old World prophetic tradition.
Redaction: Nephi’s explanation of his purpose has turned into a digressive address to his future audience. The information is certainly relevant, but this discussion of the differences between Old World and New World prophetic forms is not logically connected to an expansion of Isaiah’s themes. Rather it explains why such a discussion is necessary. This aside implies that Nephi is composing as ideas suggest themselves, not according to an already thought-out line of argument.