8 Thus we see how quick the children of men do forget the Lord their God, yea, how quick to do iniquity, and to be led away by the evil one.
9 Yea, and we also see the great wickedness one very wicked man can cause to take place among the children of men.
Mormon points out that this story has a moral: people are easily swayed, more easily than they would like to believe. We can easily be deceived, and for that reason, one persuasive individual can cause great wickedness among a formerly righteous people in a very short period of time.
Today, I will remember that I and the people around me are impressionable. As a result, I will surround myself with positive influences: people who help me to be my best self, media which inspire me to do good, and environments where the Spirit of the Lord can dwell.