Okay, writing some questions for my class, I stumbled across this, and I really have to say that the idea that the pardoner is trying to get people to address their sins is an incomplete answer. He is clearly trying to get people to purchase pardons and relics, and he isn't really concerned about their morality. In fact, when he's telling the story of the three rioters, he mentions them and then goes off for three pages about sin in general. His conclusions include the idea that because swearing comes before murder in the ten commandments, swearing is the worse sin. He even claims that Paul condemns those who eat too much as 'dross' (trash). He condemns these common sins far more explicitly than the more serious sins BECAUSE people are more likely to have committed them, and he can, therefore, get more people to buy pardons. At the end, he goes so far as to tell people they can sin every mile of their trip, and he'll be there to absolve them as long as they can pay him coin or silver or brooches or wool.
Clearly, the pardoner's purpose is to drum up business and Chaucer's purpose is to show just how corrupt the church system had become.
The Pardoner's tale is an allegory that teaches the moral of participating in avarice, gluttony, and sloth, the consequences of which lead to death.The irony, of course, is that the Pardoner is guilty of all these sins himself.