Why should esoteric organizations which study and teach the complexities of Cabala, surely the ultimate in intellectual spiritual contemplation, by bothered with Arthuriana?
The clue lies in the dating. Geoffrey of Monmouth, who was as likely to have been Breton as Welsh, wrote his largely fictional History of the Kings of Britain in Latin around 1136. The Norman-French Wace used this in 1155 as the basis for his Roman de Brut, which turns it from an heroic tale into a story of courtly romance, and also introduces the Round Table to the story. Chrétien de Troyes wrote five romances between at the earliest 1159 and the latest 1190; the last of these, Perceval or Le Conte de Graal, introduces the Grail for the first time. Perceval, though unfinished, is clearly a parable of the journey from ignorance to knowledge; the Grail is described as a mystery. The idea of the Grail being a sacred chalice, either the cup from the Last Supper or the cup which was used to catch the blood of Christ on the Cross, did not appear until Roberr de Baron wrote Joseph d’Arimathie, probably in the late 1190s. Layamon, an Englishman, put Wace’s Brut back into English, dropping much of the courtly romance, around the turn of the twelfth and thirteenth centuries. The four Continuations of Perceval, by different hands, date from between 1200 and c. 1240. Each says more about the Grail than Chrétien de Troyes did.
– A Brief History of Secret Societies: An Unbiased History of Our Desire for Secret Knowledge (1997), pp. 277-8