He uses satire in the general prologue because he seems to make fun of the fact that the clergy is supposed to help people and be spreading Gods word, but they often in that time used their place in the church for their own personal gain. The narrator describes many different characters and most of them use their power for their own gain like The Wife of Bath, who seems to use the fact that she goes to church so she seems like a better person, or the Pardoner who will grant you forgiveness for a bribe. Even the Friar who begs for money and can sweet talk so well he gets even the poorest old ladies to give him money.
