Regardless of the original source of this prophecy, and whether or not it is a citation or a paraphrase (which Jacob has demonstrated a tendency to do in this very sermon) the emphasis is on conflict against Zion, and specifically the Jew and Gentile that oppose Zion. This verse is being cited in the context of Isaiah's prophecy of the ultimate salvation of Zion by the hands of the Gentiles, so what is the purpose of the mention of the two parties who will oppose Zion?
In the context of the New World, and specifically in the social reconstruction of early Nephite society discussed for the overall context of Jacob's sermon, the Jew and Gentile opposing Zion are very significant. The reference to Jews opposing Zion become the Lamanites, and the Gentiles opposing Zion become those others in the land who also would stand against the Nephites.
It is the Gentiles within the Nephite community that are the fulfillment of the Isaiah prophecy.