Le Morte d'Arthur by Thomas Malory is not completely an original work. Instead, Malory compiled and edited together several different sources of Arthurian Legends into different books. One of the books, and the one that seems to have had the biggest impact, is the book that covers the quest for the Holy Grail.
According to Malory, the quest for the grail is conducted by all the knights of the round table, but rather than being a joyous undertaking, it is actually quite grim. Most of the knights know that they will fail along the way, and even King Arthur knows that it will ultimately be the end of his fellowship of the round table.
Malory's other books had been about the triumph and prowess of the knights of the round table, but this book reminds us of something important: as good of knights as they may be, the round table is still made up of regular men. And like all regular men, they fail. In particular, they fail in their service to God.
It's worth keeping in mind that the Arthurian legends are not explicitly religious stories, but Malory's quest for the holy grail certainly is. It also doesn't make a lot of sense as a story if it isn't for that context, so it's important to go into.
Ultimately, Malory's quest for the holy grail isn't so much about finding a holy object. In fact, there's actually nothing other than stories that are brought back to King Arthur's court. Instead, the story is one of healing, redemption, and ultimately reform.
In Malory's work, a king who has been charged with the keeping of the grail is wounded in the thigh by the Spear of Longinus that pierced Christ's side. This is seen as divine vengeance for some unmentioned sin on the part of the king, and the wound never heals, preventing the maimed king from standing. Without his leadership, the lands around the castle of the maimed king suffer as well and become a wasteland.
The end of the holy grail story is when the king is restored to health and able to lead his lands once again. A divine punishment for sin is part of the story, but is not the end. Instead, the sinful, and thus wounded, king is healed by the blood of Christ which is still on the spear. The story is meant to symbolize the saving work of Jesus and the redemption from sin.
But I also mentioned reform earlier. The knights that complete the grail quest are important, but so are the knights who fail along the way. Two of these in particular stand out in the story: Sir Gawain and Sir Lancelot. Sir Gawain, in addition to a host of other character flaws, is a murderer. That alone is mostly what prevents him from completing the grail quest, but in addition to that, he also refuses the chance to repent.
In Malory's characterization, Gawain is representative of a real problem in the round table. They are all, for one reason or another, men of bloodshed and evil, and this will ultimately lead them to destroy one another. Gawain is given the chance to change, but ultimately rejects it to continue in his evil ways. Gawain, thus becomes a symbol for unrepentant man, who, given a choice of redemption ultimately rejects it, leading to his failure in the quest.
His foil in the story is Lancelot. Lancelot is also living in mortal sin. He appears to be the best knight in the world, and he is impossible to defeat in battle. But he's also sneaking around and committing adultery with the the king's wife. This prevents him from completing the quest. However, unlike Sir Gawain, when given the chance to change his ways, Lancelot chooses to repent. His evil ways still keep him from the quest, but Lancelot comes to represent those who turn away from evil.
Both Gawain and Lancelot return to the court of King Arthur, but they bring options with them. The court can continue in it's evil the way Sir Gawain does, or they can reform like Lancelot. Meanwhile, Sir Percival and Sir Galahad complete the quest, heal the maimed king, and redeem the land. The story ends a little abruptly, but it ends here because it is a quest for holiness and redemption. Both are achieved by only two of the 150 knights that went out on the quest. The question then, is how will the other knights respond? Do they follow Lancelot's example or Gawain's?
The Arthurian legends end in tragedy. The book is called The Death of Arthur, after all. It's easy to guess what the round table ultimately chooses. Gawain's presence continues to poison the fellowship of the round table. Lancelot backslides. It all ends in sorrow, but that is a story for another day.
