Jacob quotes Isaiah 49:23 and 24. This is the text that Nephi requested, and it is clearly one that Nephi believed to be important as Nephi himself quoted it in 1 Nephi 21:22 and 23, although, at that time, Nephi inserted the entire chapter.
The Old World context is some future time when the gentiles would be important to the restoration of Israel. Scattered Israel would be gathered through the efforts of Gentiles. When the gentile kings would be nursing fathers, the imagery is of caring parents of young children who are not able to care for themselves. In Isaiah’s original context, this was a promise of a distant future when the gentiles would gather Israel. Undoubtedly, those who were scattered after the Babylonian destruction saw a literal fulfilment when the Persian king, Cyrus, allowed those of Judah to return to their homelands.
That event is still in Jacob’s future, but it is also a world away. For this people to whom Jacob reads these words, there had to have been a different way to see the application of these verses to their current situation.