This is an important point for Mormon. Mormon is writing a history of his people that shows how the foundational promise of Lehi applies to them. That promise indicates that they will prosper in the land as long as they are righteous, but they will be subject to other nations if they are unrighteous. The current trend of the Nephites is to become less righteous, and that will lead to the inevitable destruction of the Nephite polity. However, Mormon must also show how the Lamanites could not be affected by that same promise, since their father was also Lehi. Mormon emphasizes the Lamanite righteousness both in contrast to the Nephite state, and as a means of showing why they are able to come through the coming calamities while the Nephites do not. The promise of protection is symbolically shifted to the Lamanites because of their greater righteousness.
Chronological: the sixty-second year of the reign of the judges is approximately 33 BC in this correlation.