Erec and Enide by Chretien de Troyes is a slice of the legend of King Arthur, as told by the author. If you can cope with Medieval French, you should read it in the original. If that's not possible, there are modern French and English translations available, which are a lot easier to read. You should also check out the excellent study guide available on this website.

They don't call the first versions of the Arthurian legend "romances" for nothing. Before King Arthur was a superhero or the mythical father of modern Britain, he was an uxorious West Country war chieftain with a magical friend. His knights had their own loves and adventures, but all of them are copies of the main narrative. There's a knight, a woman, and an unattainable object of devotion. There's a quest, adventures, a climactic struggle, and a resolution meant to impart a moral lesson.

In Erec and Enide, the unattainable object is perfect Christian charity or love. The two main characters are already married, so there's no question of a chaste knight embarking on a quest for the Holy Grail to impress a lady, as did other knights in the Arthurian legend. Here, Erec and Enide ride off on adventures together, and their fights and meetings are steps on the way to the ultimate act of charity, in which they set free prisoners, and the ultimate "sacrifice," in which they agree to be crowned king and queen of the Kingdom of Nantes and dedicate their lives to public service, in imitation of Arthur and Guinevere.

The moral lesson which ties it all together goes something like, "Be faithful and humble, and you'll win in the end." This applies to Enide more than to Erec, who is suspicious of her throughout the story, but if you read "faithful" as "dedicated to your purpose," then you can count Eric's killing of bad knights and his making of strategic friendships. Both the main characters, each in their own way, were faithful and humble, and they got rewarded with "the kingdom," which in the story is in France but is meant to stand metaphorically for "the kingdom of Heaven."