The beauty of Chaucer's prologue to The Canterbury Tales, is that he gives us a microcosmic look at the Middle Ages. When he introduces the pilgrims, he gives us the good, the bad, and the ugly. It is a cross section of medieval society.
The Knight and Squire are the picture of chivalry.
The clergy does not fare as well. Both the Monk and the Friar do not display the values that we associate with religion. The Nun is seen as vain.
The merchant class is also represented dressed to reflect their status.
The rest of the pilgrims are a wonderful cross section of people from the Oxford Scholar to the Wife of Bath (my personal favorite) to the Pardoner. Some of these people are rude and crude while others seem to be virtuous and good.
Through his narration, we are able to get a comprehensive picture of England in the Middle Ages. Rather than somebody writing about this after the fact, Chaucer is an eyewitness to the time.