If Belief = power/existence
Wish/Prayer = method of channeling said belief.
Reality Marble formed into human form, and usable via the wheel of Tarot cards. The grail is several aspects, and therefore could plausibly be all : from cup to chalice, to rock to necklace, to platter to anything. Since the aspect is undefined, the actual existence is undefined : therefore, there is a third circle to existence. Corrupted Existence, which is the darkness that seeps into the cycle of existing, death and rebirth : Existence itself, which generates this wheel and in theory able to remove souls from this : and then Wish in itself, which is falsified creation.
Beings made of Belief are granted power as long as said belief is relevant. The ratio of belief/power depends on the level of belief/population/strength of the one believing. This is a mass amount of factors, and thus can create gods in their own rights : for as long as belief is held, belief will exist.
A nameless thing believed in will have less power but more flexibility then a named thing. For once named, a concrete image will seep around the name, and thus a concrete form. Therefore, those with names are allowed to exist rather then simple non-exist. Using pieces of all beliefs, a power can be formed to destroy the world or save it. Such is the creation of ''power'' belief of a system by Existence herself will create such things as good and evil and thus gods that spawn out of that belief and more. A belief acknowledged by Existence gives it permanent life : and thus that is how corrupted existence came into play. For the world wished of evil : acknowledging that wish tore Existence into good and evil parts in itself, thus making a Corrupted existence.
Therefore wish is the life line of the world : as long as in itself, Existence continues to believe in the world, it will exist. Perception becomes a part of this when it comes to individuals, rather then an aspect. a true wish will be granted : not in a commonly perceived view, but in the view of existence or the wish in literal self. Therefore the power sin themselves are as flexible as all.
For the link of ''wish'' and ''belief'' to the mortal world is a single, accented being, allowed to pierce into it's powers [which is the reality marble in human form according to tarot card section. May add some other things into it, such as the sins/virtues and the Realms of Resurrection.] and possess a limitless potential, making the being akin to god. However, the being will have a consciousness and a perception : although empty of personal flavour at first, this being is only the direct vessel of wishes on the plane it exists on : there are no duplicates in alternate timelines, worlds or places. For all existence, there is only one incarnation of this.