Board Thread:Questions and Answers/@comment-32975343-20170828171820/@comment-6036561-20170828173215

I'll try to explain as I've understood it... hope I'm not too much wrong :/

The Greater Grail is a sort of "prana battery", that charges itself on the Ley Line (Earth's prana, in a way). Once it's filled, its prana is used to summon the Servants from the Throne of Heroes.

The Lesser Grail (a.k.a. Justeaze and descendants) is a recipient in which the fallen Servants' souls are gathered. Once it's enough filled (it doesn't need all the seven Servant souls) it can be used to materialize the Hoy Grail.

The Holy Grail is a "door" to Akasha... let's summarize Akasha as bottomless well filled to the brim with prana - so, an infinite amount of prana. Thanks to that, the winner of the Holy Grail War can perform any kind of magic, even those that normally no one can do (in the same way a Servant can teleport thanks to the aid of the a Command Spell, while teleportation is a kind of magic no one can usually do). The "miracle" is this: the fact that thanks to the infinite mana reserve  you can became temporarily "omnipotent"