Keep in mind that there are multiple versions of the Arthurian legends, so the function of the Grail changes with the legend. The Holy Grail is blessed chalice that can provide happiness, eternal youth and food infinitely, it's a symbol of divine grace. It's role in the legend is a device for King Arthur's Knights to quest after and go in search of, as well as a healing force to some knights and a test of spiritual purity and worth.
