The Grail Vow is the most sacred oath a knight of Bretonnia can swear: a pledge to abandon home, title, and comfort and ride out in search of the holy Grail of the Lady of the Lake, never resting until he has proven himself worthy of her blessing or died in the attempt. It is the summit of the Bretonnian knightly path, and few who take it ever return.
A knight upon the Grail Quest, known as a Questing Knight, forsakes the fine living of the nobility for a hard and wandering life, seeking out the mightiest foes and most perilous deeds to demonstrate his purity of purpose. He will drink no wine, taking only water, until the Lady deems him ready. Most wander for years; many are never heard from again, their bones left in some far wilderness.
For the rare knight the Lady judges worthy, she appears at last and offers him a draught from the Grail itself. To drink is to be transfigured — the knight becomes a Grail Knight, hale beyond mortal measure, ageless, and radiant with the goddess's favour, a living saint of the realm. Such heroes are revered almost as demigods, their deeds recorded and their tombs made shrines. The Grail Vow is thus the engine of Bretonnian faith and valour: the promise that a life of perfect chivalry can raise a mortal man to something very close to the divine.