The ending of "The Knight's Tale" is really, really deep. After calling Palamon back to Athens and assembling his counsel, Duke Theseus lectures everybody, but especially Palamon and Emily, about how death is inevitable and a part of God's plan for the world. His goal? To convince Palamon and Emily to stop whining about Arcite's death and get married already. They agree to it, but you may be wondering why Theseus's long-winded (some might even say boring) speech is necessary.
Before you hit the snooze button, consider this: a lot is at stake for Theseus at this moment. It's not just that his counselors want an alliance with Thebes through Emily's marriage to Palamon (although that's a big part of it), it's also that Theseus is supposed to be the order-maker, the one who solves problems and makes his society work the way it should.
Theseus ordered Palamon and Arcite to fight a duel over who got Emily. This duel was supposed to a) end the feud, and b) get Emily married off to a suitably noble husband with good family connections. But Arcite's tumble from a horse messed up the plan. Is Arcite's death frightening evidence of the randomness of fate? Does it reveal how even Theseus, the seemingly all-powerful order-bringer, is helpless before it? If he is, then are we all? Say it ain't so! No, Theseus can't allow Arcite's death to pass without some philosophical reflection, because he can't allow the seeming randomness of it to undermine people's belief in the rules and order that keep him in power, and which he represents.
What's Theseus's spin on Arcite's death? Well, he says it's just one more example of a rule God has made – all earthly things come to an end. Arcite's death doesn't demonstrate random disorder in the world. It's actually evidence of God's stable and eternal plans. Problem solved. (Whew!)
Theseus's suggests that the proper response to death is to accept it as inevitable and move on with the business of living. This just so happens to support the marriage of Palamon and Emily that will please Theseus's counselors, as well as move Emily into her proper place as a nobleman's wife. Order restored, end of story.