The main "message" of The Knight's Tale may well be a concern with the proper ordering of the elements that compose a person's being and soul.
While there are clearly more than one theme, with the predominant ones those of Chivalry and Courtly Love, the thrust of the tale is upon the turbulent natures of the two Theban cousins, Arcite and Palamon, who find themselves taken hostage by Duke Theseus of Athens. While they are imprisoned, both men fall in love with the daughter of the Duke, Emily who walks outside. When Arcite is freed one day thanks to the intervention of a friend, he is told he must leave the city. Now he feels that the imprisoned Palamon is more fortunate because he can, at least, still see Emily.
So, Arcite disguises himself and returns to Athens to be a servant to Emily. But, later, Palamon escapes and hides in a grove of trees. As he stands there, he overhears the disguised Arcite bemoan aloud his unrequited love for Emily; so Palamon leaps at his cousin, the argue until settling upon having a duel. Arcite promises to return the next day with armor and weapons.
As the cousins duel the following day, Duke Theseus sees them and orders them to stop; then, infuriated as he recognizes them, he orders the two men put to death. But, his wife Hippolyta and Emily implore him to show mercy. So, the Duke of Thesus, who becomes symbolic of justice and reason, intervenes. He decides that the two men must return for a joust in a year's time with one hundred men.
After the year passes, the men return. Before the joust, Palamon prays to Venus to grant him Emily; Arcite prays to Mars for victory in the joust; Emily prays to Diana for eternal virginity. Ironically, the men receive their wishes, but Emily's is denied. They, then, are established as the dominant forces.
- Palamon loses the duel to Arcite, but he wins Emily after Arcite dies.
- Arcite wins the battle; however, he loses his life when an earthquake causes his horse to throw him and crack his head. He dies and, therefore, loses Emily.
The Knight observes near the end,
"Who makes and drives our living and dying but the king
Of this world, great Jove, the cause of everything,
Turning whatever grows back to the source
From which it derived, and where it belongs? And of course
No living creature, no matter its stature, has force
Enough to resist any of great Jove's laws.
And, so with the ironic outcome for Arcite, Palamon, justice is re-established as the men actually receive what they wish for.