Chapter 49 closed with a righteous people being preserved by Yahweh’s hand. Mormon spelled out this conclusion as proof of the Lord’s protection upon a righteous people. He here shows the rest of the promise’s fulfillment—their “prospering” in the land. Mormon sees being “exceedingly rich” as fulfillment of their covenant with Yahweh. There is nothing inherently wrong about the riches; but the lesson of the past is that riches lead to costly apparel which leads to social classes and pride. Internal tensions as the people desire more of the worldly values that accompany riches are virtually inevitable.
Reference: Mormon again recites the foundational promise of the Nephite people. Lehi had articulated this promise (2 Ne. 1:9, 4:4), as had Nephi (1 Ne. 2:20, 4:14) and Alma (Alma 9:13, 36:1, 38:1). This promise is easily the most frequently referenced of the purely Nephite scriptures, and rightly so. It is the Lord’s original promise to Lehi’s descendants.