[Arthur] charged them never to do outrage nor murder, and always to flee treason; and to give mercy unto him that asked mercy, upon pain of forfeit of their worship and the lordship of king Arthur; and always to do ladies, damsels, and gentlewomen and widows service, to strengthen them in their rights, and never to force them, upon pain of death. Also, that no man fight a duel they knew was wrong, neither for love nor for worldly gain. So unto this were all knights sworn who were of the Table Round, both old and young. "And every yere so were the[y] swome at the high feste of Pentecoste."Pentecost was the day when the Grail Quest began, which destroyed the might of the Round Table. The Grail visited Arthur's table at the feast, and then passed away again. Instead of accepting the grace offered, they quested after it as if they could win it by their own valor and worthiness, and so were destroyed.
Pentecost is the right day for that message. Before the time of the apostles it had been the feast of firstfruits. If early spring represents the return of fertility, early summer allows us to see the first children that come of that renewed fertility. It is the first nourishment that comes to us after the winter. There remains a long summer ahead before the full harvest -- summer was the hungry time, in the middle ages. Yet here is a first taste of grace, and a promise of greater grace to come.
Arthur did not go on the quest for the Grail, but stayed true to his duty to keep the walls of this world.
And therewith the king said: Ah, knight Sir Launcelot, I require thee thou counsel me, for I would that this quest were undone, an it might be Sir, said Sir Launcelot, ye saw yesterday so many worthy knights that then were sworn that they may not leave it in no manner of wise. That wot I well, said the king, but it shall so heavy me at their departing that I wot well there shall no manner of joy remedy me. And then the king and the queen went unto the minster. So anon Launcelot and Gawaine commanded their men to bring their arms. And when they all were armed save their shields and their helms, then they came to their fellowship, which were all ready in the same wise, for to go to the minster to hear their service...
And then they put on their helms and departed, and recommended them all wholly unto the queen; and there was weeping and great sorrow. Then the queen departed into her chamber and held her, so that no man should perceive her great sorrows. When Sir Launcelot missed the queen he went till her chamber, and when she saw him she cried aloud: O Launcelot, Launcelot, ye have betrayed me and put me to the death, for to leave thus my lord.It is a grave question that troubles me every year: is it right to go on the quest, or is it not? Lancelot holds that it is better to die in that quest than in any other fashion. Death is sure to us all, but the suffering of the quest prepares and purifies the spirit, so that it might be a little less unfit for the presence of God.
Arthur holds to his duty to keep the space in this world in which joy is possible, and trust in the coming of the later grace. So he held Camelot, and the peace of the land and the people, while his knights broke themselves in the wilderness.