Since I can't figure out what to say about chapter 26, I have decided to quote from Dianne Bergant's comments in the New Interpreter's Study Bible: "Ben Sira was a man of his time...." and "[We] must discover ways of gleaning the fundamental theological meaning of the teaching in order to interpret it in ways that are more suitable for our times."
Chapter 27: Don't betray your friend's secrets. Don't waste your time with foolish people. Treacherous people get what they deserve.
Chapter 28: Let the Lord take care of vengeance. You forgive. Don't gossip or lie or slander.