Stating the question broadly: In a world where healing magic is available, why isn't the social structure different from what we know of the middle ages? The implicit assumption is that the widespread use of healing would extend the lifespan of everyone in the setting, not just the adventurers. Why should a king ever be assassinated if the local high priest can resurrect him? These questions of social stability plague my mind, since the very way in which human beings interact with one another or conceive of social position would inevitably change.
My answers are multifarious, as I've stated above. The confluence of the following setting-assumptions keeps healing magic from overwhelming the established social order:
- Not all priests have the ability to commune with their gods. (This may stand to revision now that I've read the 1e rules in the DMG describing the low level clerical spells, namely 1-2, being empowered by the rituals learned by priests... though, the more I think about it the more I think I will simply say that those rituals are only learned by those novices who show aptitude and desire to take on the additional sacred duties) This means that of the many priests in a locale, only some will have a class.
- The gods are jealous and strict with magic, reserving its use for those who pledge themselves to one cult exclusively, which is a small segment of the population.
- The law of the pantheon, as enforced by its beneficent autarch, prevents gods from becoming flagrantly involved in the lives of mortals except through the official and approved channels of the clergy.
- Powerful magic is difficult to access, and takes a real toll on the priest and the god. Thus, it is not waved around and applied everywhere it could be.
- Resurrection is against the code of the Gods, and must be cleared with Akem the Gatekeeper, who is notoriously cranky and rarely lets anyone return to the Middle World. As the Papyrus of Anki states: "The Gates of Death are closed."
So, these facts restrict the massive use of healing magic that would break down a lot of normal assumptions about life, living, and society. Kings who are assassinated cannot be returned to life because their souls are jealously guarded by Akem, who sends them on to their proper rewards but almost never returns them to the world above.
Between the dictates of Haeron, the chief god of the mannish pantheon, there is to be no bestowing of spontaneous miracles and priests are to be rewarded for their devotion. This is one reason why dedicated priests cannot access high level magic as soon as it would benefit their patron; the other is that their minds are physically unready for that level of power, and were a god to dump it onto them it may very well annihilate them in an orgasm of glorious light and energy.
But what about the High Priests of the faiths? Can they attain this station even if they're of low level? It would suggest a failure to align oneself properly with the Godhead as well as the inability to channel the most potent forces of the god. However, the appointment to high offices of faith is generally a political matter at least as much as it is a religious one. Could a reformer with little practical experience in enacting miracles hold that office?
It seems to me that there must be a way for non-classed priests to gain experience through service to the temple. However, it also seems that yes, non-casting priests should be able to hold high office, though it may not be the solution that deity would desire. After all, isn't it worth having a prime servant who can manage and save your temple, even if he can't manifest potent miracles? This relies, of course, on the assumption that the priest must be mentally and physically capable of achieving the higher ranks of magic before they are unlocked to him. If this precept were false, any god could grant any spell to any one at any time (but doesn't because of various reason). This would mean that the leader of any faith would be a de-facto level 15 mythos priest in addition to any other class he might have.
I reject this as a matter of both worldbuilding as well as class sense. I don't want a level 12 fighter who is also an ordained priest to be elected to be High Lawkeeper and suddenly rocket up to the powers of a level 15 Peaceward. Which means, then, that I don't want any god to grant any spells to anyone, so I'll keep the dictate stating that priests must grow into the use of powerful divine magic or it will eat them alive from the inside.
Still, doesn't it make a kind of sense that classed priests can gain experience by going about mundane jobs in the temple? The other option (that classed priests can only gain xp by killing people and/or fulfilling their dogma with magic) would limit high level priests to adventuring to get to their rank. I can't imagine that ever level 3 or level 6 priest had to go out and kill monsters (or fight in a war, or something of that nature) to gain access to his magic. Therefore, it must be true that they can garner xp in some way other than by exercising their powers on the road.
Even as I typed that I think I may have found an equitable solution that doesn't bend any rules and doesn't add any ones. Priests receive 200xp (by the 2e DMG guidelines) for casting spells that "further their dogma." One would assume that casting these spells for the service of their temple would count as doing this in the pursuit of the god's dogma—thus, any time a priest were to cast a spell for his temple, he would receive 200xp. After all, shouldn't the ability to cast higher level priestly spells be predicated on the use and exercise of the very "muscles" (in this case the flexing of the things which allow the priest to contact the divinity at all)?
Of course, I might supplement this with experience for NPCs from meditation and deep study of the holy mysteries. After all, it takes gads of experience for a mythos priest to reach level 15—for the sake of the argument and because I'm at work, let's say 45,000xp which would necessitate a lifetime casting of 225 spells all of which directly furthered the work of the god. Granted that a sedentary priest might cast, say, 1 spell a month and perhaps half of those would actually count, that leaves an average of 37.5 years before they reached level 15...
Actually, that's not all that bad. Jigger the numbers a little, and there might be something to that.