Thoughts on what powers clerics
by LoZompatore.I'd say that "Bestow" is not the spell used by Immortals to grant spells to their clerics.
Actually WotI's rules provide an answer to this, albeit several references must be assembled to get the full picture.
Below I'm always making reference to " Codex of the Immortals" manual.
Page 75, "Provide Power and Guidance to Clerics, Paladins, Avengers and Mystics" section states the following:
"Immortals... provide spells to their clerics (and paladins and avengers) automatically, without having to spend any time at all. However, most do meditate at some point each day in order to use their 'Immortal Eye' spells to see what's happening on the world and to cast 'Hear Supplicants' spells to find out what their mortal followers are praying for. During this time, they can choose to deny spells to clerics who have displeased them, a decision which takes only an instant and requires no power expenditure."
Notice that the act of providing spells to clerics does not requre time to be put into effect (so it is not a spell, as opposed to the two spells detailed in the following), and also the fact that the act of denying clerical spells to the unworthy does not require time and power expenditure. I would also add that such an act does not provide any power gain (i.e. some power returning to the Immortal for the clerical spells that will not be cast).
So I would say that the act of granting clerical spells does not require power expenditure by the Immortal, and it is part of how the Multiverse is shaped.
Possibly the Immortal act as some kind of catalyzer of clerical energies already present in the Multiverse, diverting part of them to his or her worthy followers to allow them to cast spells, but the Immortal is not actually the ultimate source of such powers. This would also align with clerics casting spells but not following any specific immortal (like the People's Temple, the lawful/chaotic/neutral brotherhoods of the Savage Coast, the nature-worshipping people of Ulimgengu and druids in general).
Moreover, there is the following on page 80:
"Creating and commanding clerics. A character who has just gained Immortality does not yet have any clerics. He or she must search the world in Incorporeal Form to find some likely young charcaters, enter their dreams, and thell them that they should devote their lives to espousing his or her faith and philosophy. If they respond favorably, these mortals will become his or her first clerics."
Again, no power expenditure by the Immortal is mentioned when gaining clerics.
What is written on page 83 is most interesting, in my opinion:
"Fading
The link between Immortals and their followers is not well understood, even by the most knowledgeable Hierarcs, but all Immortals are aware that without a following, they can slowly fade awat into nothingness.
...
This fading begins a full year after the Immortal's last mortal follower dies or abandon his or her faith. It takes ten years for the Immortal to fade into nothingness.
However an Immortal who has faded to nothingness is not dead; ho or she still exist as a dim and undetectable life force on his or her Home Plane and can be revived if the conditions are right. If later-day mortals discover ancient writings about this Immortal and decide to follow his or her teachings and devote themselves to his or her philosopies, he or she will hear their call and awaken. The newly-revived Immortal will once again be a 1st level Initiate, but he or she will be Immortal again.
Initiate Immortals who serve the higher-level Immortals who acted as their sponsors share the benefits of their sponsor's followers until such time as they end their service. Independent newly-Immortal Initiates tend to be very busy in their first decade creating a mortal following."
"Immortal Loss and the effect on Clerics
When an Immortal is truly killed, or trapped in another dimension, or imprisoned by baaka, that Immortal can no longer provide spells to his or her clerics. The clerics will wake up one day and their meditations will grant to them no spells; if one still has a 'Commune' spell, it will not work. Naturally, the Immortal will not be able to provide guidance to his or her clerics and followers. The crisis of faith following his or her apparent abandonment of them will cause his or her clerical following to fall away and die out, sometimes resulting in the Immortal fading as described in the preceeding section.
For this reason the most cautios, wily and responsible Immortals tend to create artifacts which will still provide spells to their clerics, paladins and avengers even when the Immortal is in another dimension, imprisoned or even slain. For more on how to craft such an artifact, see page 99."
An so, on page 92 mid of central column we have the, "Spell Generation" power for Artifact creation, cost 250 PP.
As written above, description of this power is on page 99, third column:
"Spell Generation: This power activates itself on any day when the Immortal creator of the artifact fails to provide spells to his or her clerics; this power perform this function instead. It also allows the artifact's current "owner", if a spellcaster, to memorize one additional spell at each spell level he or she already knows."
So it seems that a 250 PP "entity" is able to provide clerical spell at no cost to an undefined (potentially unlimited) number of clerics aligned to it.
As the lowest power level for an Immortal is Initiate Level 1 at 300 PP, I would say that they have enough personal power to provide clerical spells.
So, summarizing:
New Immortals start with no clerics but they should start attracting some followers within 1-10 years otherwise they will fade. On the opposite, there exist clerics that do not follow specific Immortals and gain their powers from nature, philosopies or other general principles like alignment.
Immortals grant or remove clerical powers at will without power expenditure and can create a 250 PP artifact that can do this job for them in case they are incapacitated.
All of this, in my opinion, implies that Immortals are not the source of clerical powers. Instead, Immortals represent just a way - and not the unique one - to channel such power (that we must assume should be kind of raw, primeval and diffused everywhere in the Multiverse) on selected mortals following a definite ethos; such mortals, in turn, contribute with their faith to keep the Immortal "real" and prevent its fading.