Jacob continues with his personal knowledge. Speaking specifically of those carried off from Jerusalem, he indicates that they should be returned again. It is interesting in passing at this point that Jacob does not specifically mention the role of the gentiles in this return - even though the gentiles are specifically mentioned in the verses from Isaiah that he uses as a springboard for this exegesis. There are two reasons. The first is that the particular verses in Isaiah refer to an event yet future to the return to Jerusalem, and second that there is another use Jacob may have for the reference to the gentiles - a usage perhaps related to his insistence that while he is speaking of Jerusalem and future events in Jerusalem - he is yet speaking and directing these remarks at a current and present population.
Jacob's prophetic discourse moves rapidly from the return of the Jews to Jerusalem to Christ's mission among them. Clearly if he was to highlight the critical foundation of their society - that is the destruction of Jerusalem, he must also have them return before he can discuss the mission of Christ in Jerusalem.
Anthropological information: The exegesis of Isaiah will depend upon this revelation of Christ - but the vision of the destruction of Jerusalem had to be (in the terminology of anthropology) a foundational "myth" for the Nephites.
I should explain that by "myth" there is no implication that such an event did not take place, but rather that it was such an important event that it was a part of the information that structured and gave meaning to their society. For the Nephites, the destruction of Jerusalem was the explanatory "myth" that gave them the reason that they were in a new world, and creating a new society.