The Cleric Problem

The Cleric class started life as a pastiche of Peter Cushing's portrayal of Abraham Van Helsing in Hammer Horror's Dracula movie.  I love that movie.  Dave Arneson was very liberal in using '70s pop culture in his early roleplaying sessions, and in one game he had been playing with two teams against each other where one of the players created an evil vampire named Sir Fang who had become too powerful to stop, so the proto-cleric class was created as a counter.  When Gary Gygax included the class in the original Men & Magic booklet, he retrofitted them to reflect the Crusaders of Militant Religious Orders and tasked them with the power of turning undead and casting miracles.  Mechanically, they were the midway point between the Fighting-Man and Magic-User classes with a unique spell list which included 3 healing spells and the ability to resurrect allies from the dead, which lead to the unintended consequence of their role being reduced to healing bots.

The problem came when Gygax's players asked the natural question "Where do the Clerics' powers come from?"  Gary Gygax's flippant answer was originally "the gods" but as his players pressed the issue, he created two fictional dieties, St. Cuthburt and Pholtus, and then eventually antagonistic dieties, and then it spiraled out of control into a whole pantheon and cosmology based around alignment charts and planar existence and spheres of power, and other assorted overly complicated junk.

Every OSR blogger trying to make a retro clone or attempting to streamline their own game has tackled this problem one way or another.  Some throw out the Cleric class altogether, others change their nature into being some kind of atheist heal bot, and yet others go down the 5e path of giving each Cleric a unique spell list dependent on the individual god they serve.  To me, these are all bad solutions as they solve a problem by creating even more problems, are based on an erroneous understanding of mythology, and tend to dilute the essence of the class.  And it all comes back to Gygax's misstep in mentioning that a Cleric's powers came from "the gods".

Now, Gary Gygax has stated that he felt that including real world references to God and Satan were inappropriate for a role playing game. I read an anecdote of a group where the DM stipulated that Cleric players had to pray to the actual God for their abilities, and it caused an uneasy awkwardness at the table. So I totally agree with that sentiment and even revised my own homebrew setting to throw out references to real world churches and religious organizations, but a really elegant solution was hiding under our collective noses the whole time.

According to some Christian traditions, Saints who are thought to be in Heaven can intercede on the behalf of parishioners and are prayed to themselves. Though there was a real, historical St. Cuthbert, the one invented by Gygax bears no relation to him and can easily be a purely fictitious patron for Clerics and other religiously motivated characters. And for antagonists, the Monster Manual is full of lists of Devil Princes and demons for evil clerics to beg for favor.

Personally I cannot conceive of a world set in the Middle Ages that doesn't have a strong Christian influence in everything from deed, to dress, to song, to architecture.  Every fantasy world tries to handwave that away, and I feel that it cheapens the setting a bit. Settings that rely on a pantheon of gods would better reflect the Roman world of Classical Antiquity than the Medieval Era.

This method of using St. Cuthburt as a stand-in for a religion that mimics, but isn't explicitly Christian, creates an elegant context for the Cleric's spell list and abilities, and a justification for the existence of the class.  Having religious characters as a player class adds an element of immersion to the game, beyond just having holy men and priests as background NPCs.

So, in my setting, there exists only one deity, however nobody prays to that deity directly.  Instead the Patron Saint of the land is St. Cuthburt, and all faithful direct their worship to him as an intercessor on their behalf, and the devoted seek to gain his blessings and favor.  Those blasphemous that seek unholy power would be fallen Clerics that have studied the teachings of St. Cuthburt, but seek to corrupt and reverse them for selfish means.  The knowledge such used could be used to summon demons and devils from the lower planes.  Druids and Rangers, who take neither side in the battle between good and evil, instead call upon the animistic spirits of Nature.

This resolves neatly with the alignment chart, as St. Cuthburt would dominate the Good alignment and Nature worshippers would have to remain Neutral, and followers of other beings would fall into the Evil categories. It also fixes Alignment Language into something understandable - the language of Law and Good would be the language used by the Church in formal discourse, as a stand in for Latin, the language of Neutrality would be the words spoken to commune with Nature, and the language of Evil would be reversed and corrupted forms of the language of Good. This would also explain why evil clerics are subject to the same weapon restrictions as their good counterparts, because to do so otherwise would rob them of their power.

tl;dr to fix Clerics, use a monotheistic campaign setting.  All worship is based on the Good/Evil alignment axis. The patron for Good is St. Cuthbert, for evil Asmodeus or any other devil prince, for Neutrality is Nature animism. The class breakdown follows:
Clerics and Paladins: St. Cuthburt, and Paladins can only be Lawful Good.
Druids and Rangers: Nature worship
Evil Clerics: Corrupted teachings of St. Cuthburt.

links:
http://blackmoormystara.blogspot.com/2011/01/bishop-carr-first-d-cleric.html