According to Christian folklore, Christ communicated certain words relating to the Eucharist to Joseph of Arimathea, who was described as a secret disciple in John 19:38, and these words were committed orally from keeper to keeper of the Holy Grail. In Robert de Borron's (ca. 1170-1212) metrical romance, Joseph of Arimathea, material power is added to the spiritual efficacy of these words, and whoever could acquire and retain them had a mysterious power over all around him, could not suffer by evil judgments, could not be deprivated of his rights, and need not fear the result of battle, provided his cause was good.
The words were the secret of the Grail and were either incommunicable in writing or were written only in the Book of the Grail, which, de Borron implied, was itself written by Joseph of Arimathea. These words are the chief mystery of the Lesser Holy Grail, as the prose version of de Borron's poem is called. They were most probably a form of eucharistic consecration, and there is evidence that the Celtic church, following the example of the Eastern Church, used them in addition to the usual consecration as practiced in the Latin Church, which is merely a repetition of the New Testament account of the Lord's Supper. The separate clause they are supposed to have formed was called Epiclesis and consisted of an invocation of the Holy Ghost.
De Borron's account also ties the Grail to Glastonbury, a borough in England that had also been identified with King Arthur by the reported discovery of his body and that of his queen, Guenevere. According to de Borron, the Grail was to be conveyed to the Far West, to the veils of "Avaron" (i.e., "Avalon," i.e., Somerset).
Furnivall, F. J., ed. The History of the Holy Grail … from the French prose of Sires R. de Borron. London: Early English Text Society, 1874.
Lacy, Norris J. The Arthurian Encyclopedia. New York: Farland, 1986.
Waite, Arthur E. The Holy Grail; The Galahad Quest in the Arthurian Literature. London: Rider, 1933. Reprint, New York: University Books, 1961.
Weston, Jessie L. The Quest of the Holy Grail. London: G. Bell,1913. Reprint, London: Frank Cass, 1964.
"Secret Words." Encyclopedia of Occultism and Parapsychology. . Encyclopedia.com. (November 20, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/secret-words
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