THE TRUTH OF THE HOLY GRAIL EXPLAINED SIMPLY
Questing for the Grail is tantamount to questing for enlightenment. The grail is just another metaphor for enlightenment or nirvana. The proof is in the choice of the symbol itself.
The Grail is a symbolized as a cup. In spiritual circles, the process of attaining enlightenment is likened to emptying oneself of oneself. Spoken another way, enlightenment is the equivalent of pouring out of your soul everything that you think you are so that God can come and fill up your soul with what you really are.
The process is symbolized as emptying a cup full of dirty water only to have it magically filled with clear Divine water by some unseen limitless Source, which also keeps the cup filled no matter how much one tries to pour out the clean water to a thirsty world.