There are quite a few Masonic theories concerning the Grail and most of them are summed up with a conspiracy of (a) The Catholic Church, or (b) The Knights Templar who covered up or hid the actual truth of the Grail and it is located in either Britain of France. The thing that gets me on these theories, is that if they are true, then the people who were responsible for covering them up didn't do a very good job because of all the theorists who claim to have the one true answer.

I subscribe to the theory that the Grail is a symbol heldover from earlier Celtic mythology of the Apollo/healer archetype. In Irish myth, there was a member of the Tuatha de Danaan named Diancecht who when asked by Lugh of his abilities, he replied "Every man that is wounded, provided that his head has not been cut off, or at least that the membrane of his brain or spinal cord has not been cut, will be completely healed by me for the combat of the next morning" (Markale, 70).

The tale goes on to say that it was Diancecht who gave the King of Tara, Nuada, his silver arm, but Diancecht's son Miach went further to chop the King's arm off and he healed it in 3 times 9 days. In a bout of jealously, Diancecht first cut the skin of his sons head, who simply healed himself. Then Diancecht cut his son's brain, but Miach again healed himself. Finally, Diancecht cut him again, this time reaching his brain and killing him.

All of this is related to the Fountain of Health of Irish myth. It was Diancecht and his two sons and daughter -Octruil, Miach, and Airmed - who would sing incantations to a fountain named Health. This motif appears again in the Mabinogian, where the Grail was depicted as being the cauldron of Bran Venigeit, where if a man was mortally wounded, he could be cured by dipping his mortally wounded parts into the cauldron.

A relief on the Gundestrap cauldron also depicts defeated men on the left march towards a picture of a giant dipping men headfirst into a pool. To the right, soldiers ride off on horseback. This motif is evident in many other myths, but I will cut this off here.

*Source*

Markale, Jean. The Druids: Celtic Priests of Nature. Inner Traditions Intl. Rochester, VT. 1999. (pp. 68-71).