In this chapter, the Fool says (not necessarily to Hobbes himself) that there is not really any such thing as justice. He says that people might as well just do whatever is useful for them. The Fool argues that there is no reason that people should keep their word and adhere to the terms of the covenants or contracts that they have made.
This is in direct contradiction to what Hobbes gives as the third law of nature. The third law of nature says that people must follow the terms of the agreements that they make. This, to Hobbes, is justice.