Moroni had given orders that the prisoners should be kept so that they might be exchanged (Alma 52:8). Ammoron now opens that opportunity.
Social: The ravages of war may be seen in the reasons Mormon gives for Moroni’s joy at the offer of exchange. One of the reasons for joy is that he will no longer need to feed the Lamanites, and may use that food for other people. This is a telling reminder that this has been a hard year for the crops, and that there is some level of famine in the land. Moroni does not begrudge feed the Lamanites because they are prisoners, but because there are Nephites who are also in need who could be fed with what is going to the Lamanite prisoners. The depletion of Nephite military strength is also implied in Moroni’s joy at the prospect of bringing back Nephites who might return to the lines.
Chronological: The beginning of the twenty-ninth year would be approximately 65 BC in the correlation used in this commentary.