Properties of the Grail in the story:

*it leaves behind a powerful EMF signature, even after it’s gone from the safe where it was kept
*it glows in the presence of the worthy OR BETTER the worthy can see it for what it is–kind of a “he who has eyes let him see” kind of thing. It glows ”very” brightly in the presence of angels.
*most of the time it appears to be an ordinary clay cup (or stone or dish, depending) but when it’s at its full power it appears to be made of gold and encrusted with jewels. (Like the boys, it’s best when it’s in use to help others.)
*it does not convey power itself: it’s only as powerful as the person who’s using it
*it’s powered by love. The more love a person has, the stronger the Grail’s power is.
*it heals: physical, spiritual, emotional wounds.
*when it’s being wielded by someone with great love, it fills with sweet water.
*it is a living object: Joseph calls it “old friend” and it warms when it needs to confirm something or is being held by someone it likes. Basically, it’s a silent character.
*it’s a door between worlds: it acts as a conduit between God and man. Without it on the Earth, it’s even harder for man to reach God.