Whyte's story focuses on a pair of converging storylines--the education of the young Arthur by the scatterbrained yet infinitely wise Merlin, who transforms the young king into various animals to teach him the many facets of human nature (Part I, "The Sword in the Stone"). Arthur's education manifests itself in the creation of a set of ideals, founded on the belief that Might does not equal Right, which run at odds with the brutal, unfair regimes set up by the despotic rulers of the Dark Ages in which he lives.
Weaving into Arthur's story is the tragic tale of Launcelot. Portrayed as an ugly boy haunted by the demons of his childhood, Launcelot pours himself into his training to become the best warrior/knight in the world. Of course, his great passion for Guinevere and subsequent betrayal of Arthur undoes him and opens up the first fault lines that lead to the collapse of Camelot. And yet, Launcelot is just a man, so we can sympathize with this betrayal.
Whyte's story is told simple and direct, in contrast to the ornate prose of Malory and Tennyson. As a result the characters are more human and modern, replete with foibles and quirks. Whyte also strips away the romance in his accurate depiction of the squalid conditions of the period. As much as I daydream about it, the Dark Ages and Medieval Europe is nowhere you'd really want to live.
More than all this, The Once and Future King is brilliant for its portrayal of universal truths, philosophic meditations on subjects that range from aging, to the nature of conflict, earthly passions, and religion, and man's inability to ever enter a state of grace. It spoke to me on levels few books ever have.
Whyte offers several explanations for why the human race is fated to remain in eternal conflict: Suspicion and fear; possessiveness and greed; resentment for ancestral wrongs. These problems are either so deep-seated in human nature, or so old, engrained, and persistent (witness the religious and tribal conflicts in the Middle East, thousands of years old and seemingly without any hope of resolution, for a modern parallel), that they are beyond the scope of mankind to solve. Even great thinkers and peacemakers like Arthur can't eliminate them--the life of one man, even a great man like Arthur, is too short, and he (and we) literally age and die before we can offer solutions.
But even though Whyte's view of mankind is bleak, he offers the hope that we can redeem ourselves through education; if we pass on knowledge, stories of great men like Arthur, we can learn from their greatness and mistakes and elevate ourselves from our baser nature. This is Arthur's promised return, not as a man but as a concept of something great that once was, and can be again. This literal passing of the torch is told in "The Candle in the Wind (part IV)," the brilliant conclusion to the novel.
In a poignant and memorable final scene the aging Arthur sends a young page, Tom of Rewbold Revell, off from the final battle at Camlann with all Arthur's letters. Arthur is to die in combat against Mordred's forces, and Tom represents the bearer of the king's flickering flame of hope and wisdom. We as readers understand that Tom will be the only survivor, and is charged with passing on the king's knowledge and preserving the story of the greatness of Camelot.
This Tom is, of course, Thomas Malory, who will go on to write Le Morte d'Arthur. All has not been in vain, and Malory (and Whyte) have left us with a shining example of the greatness we as humans--with all our faults, foibles, and failings--may yet achieve.