His basic message is that he met up with lots of people all going to the same place--which happens in April since that's when they get "pilgrimmage fever"--and they have decided to play a game of story telling on the way for entertainment. The winner is voted on by the all the participants and they will chip in to buy this person a meal at the Inn when they return. He also tells us that we shouldn't be mad at him...he's only reporting what he sees and hears...they aren't his words. Ha! He is not dumb (as he implies) and he knows exactly what he is doing by criticizing almost every traveler in the group. It is the first social criticism if a reader would be honest enough to recogize his own faults and work to change them.
Chaucer uses the prologue of his story to "set the stage". He wants to introduce all of the characters and to establish two things: 1) they are meant to represent some aspect of Medieval society; and 2) they are still individual people with their own quirks. Chaucer, not naming himself, is making it clear that he is there only to report on the stories that are presented, and not to judge. However, with the somewhat exaggerated and jocular descriptions provided, Chaucer's message is that these tale will be a light-hearted one. Like much of the satire that would come hundreds of years later, Chaucer conceals criticisms about his society under humorous anecdotes.
The narrator Chaucer is naive...he first sets out to categorize the pilgrims to Aristotle's Categories...he wants to remain very objective and philosophical, however, he fails, as all eventually do, and gives into subjectivity. When he meets the monk he realizes people cannot fit so easily into these categories and the ideals fall apart...