This comment has particular meaning to Nephi. As he explains elsewhere, the American continents (as we call them) are in reality one of the “isles of the sea.” [Jacob] will expound at 2 Ne. 10:20:
“And now, my beloved brethren, seeing that our merciful God has given us so great knowledge concerning these things, let us remember him, and lay aside our sins, and not hang down our heads, for we are not cast off; nevertheless, we have been driven out of the land of our inheritance; but we have been led to a better land, for the Lord has made the sea our path, and we are upon an isle of the sea.” (Emphasis added.)
Nephi sees in this reference an allusion to his people and their circumstances. He also sees it as relevant to his latter-day audience. This latter-day audience recovers the record and first publishes it in the Americas. We think of “isles” apart from continents. Nephi corrects that. Insofar as Nephi’s use of the Isaiah materials is concerned, the Americas are part of the isles and this message is directed to residents of the Americas.