The point of this tale is to teach an overarching lesson or theme that you must watch out for those who are too cunning or too skilled. The primary example of this is Nicholas. He is present as "sly" and "very artful". In other words, Nicholas was extremely smart and smooth. Chaucer likely included this tale as a means to entertain with a dirty story and teach a lesson on why we should be careful around people. The theme of cunning and cleverness cannot always be trusted is that lesson. This is shown when Nicholas "beguiles" the carpenter and runs away with his wife.