"The Merchant's Tale" by Geoffrey Chaucer does not contain a moral message. The story is a parody on the morals of the medieval English aristocratic society. The comic genre that Chaucer uses in "The Merchant's Tale" is called "fabliau."
The comic genre of fabliau usually revolves around everyday actions that are entwined with tricks and ruses. In "The Merchant's Tale," Chaucer focus on the relationships between a 60-year-old knight, a young woman and a young man. The old knight wants an heir and decides to marry the young woman. After the two are married, the young woman falls in love with a young man within the old knight's household.
When the old knight goes blind, he orders his wife never to leave his side because he is worried she may run off with a younger man. The young woman and the young man concoct a plan by which they can have sex without the old knight knowing. Through an elaborate ruse, they are able to have sex in a pear tree while the blind knight waits below. The knight's sight is restored by divine means, and he spies the couple in the pear tree. The young woman comes up with an excuse through divine inspiration, and the young couple is spared. The story is interpreted as Chaucer's commentary on the unrealistic ideals of the English aristocracy.