This entire chapter is an editorial commentary by Mormon, the historian, after thinking about the last chapter dealing with the Nephites and Lamanites around 7 B.C.Mormon had seen this very same pattern of self destruction in his own day among his own people. But he wants to emphasize how anxious God is to bless the people in spite of their fickle and unsteady nature.
Mormon marvels that the people cannot endure prosperity very long. They turn away from God and indulge themselves in the very things that will rob them of their blessings.