Here are the 2e flavors for the Templar. How you feel about the implied flavors and mechanics?
Dark Sun Boxed Set
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Clerical Magic
On Athas, there are several different types of clerics. Each of them pays homage to one of the four elemental forces − air, earth, fire, or water. Of course, the latter are perhaps the most influential on our thirsty world, but all are powerful and worthy of respect.
Another group of people call themselves the druids and, at least by most accounts, are considered to be clerics. Druids are special in that they do not pay tribute to any single elemental force, but rather work to uphold the dying life force of Athas. They serve nature and the planetary equilibrium. Many people consider it a lost cause, but no druid would ever admit that.
In some cities, the sorcerer-king is glorified as if he were some sort of immortal being. In fact, many such rulers are actually able to bestow spellcasting abilities upon the templars who serve them. Are they truly on par with the elemental forces worshiped by clerics? I think not.
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Priest Classes
There are three types of priests on Athas − clerics, templars, and druids.
The cleric is a free-willed priest, tending the needs of the local people with his particular talents. On Athas, clerics draw their magical energy directly from one of the four elemental planes: earth, air, fire, or water; not from any manner of deity. A cleric may be either a freeman or a slave.
The templar is a regimented priest devoted to a single sorcerer-king. Such disciples work within the hierarchy of that particular sorcerer-kings clergy, advancing in power and position. A templar draws his magical energy through his sorcerer-king. A templar can be either a freeman or a noble.
The druid is a priest tied to a particular feature or aspect of Athas. Unique geographic features are guarded by spirits when druids serve. For example, a pooled oasis has its own spirit and a single druid will reside there to protect it and preside over its use by humans, demihumans, and animals. Druids can be from any social class.
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My first thought is. A 5e Druid isnt a Cleric. But they can be both divine. So a 5e update might refer to this section as "Divine Magic", rather than "Clerical Magic".
My second thought is. Wait. Templars are NOT "on par with elemental clerics". Perhaps the Templar spell slot levels tend to be less high than the elemental Cleric spell slot levels? Perhaps Templars make more sense as divine Paladins, after all. A priest background can make sense, in relation to a specific sacred community, and in the case of the Templar, a position in its bureaucratic hierarchy. (Mechanically in 5e, somewhat countertuitively, it is useful to select a background that is redundant, because if the character already has the skill or other proficiency, the player can pick ANY proficiency instead! So a redundant background opens up options for more customization.) So, I kinda like Templar Paladins, typically with a priest background. So the three 2e "Priest classes" can become three 5e "divine classes": Cleric, Druid, and Paladin.
My third thought is, avoid the ethnocentric term "worship". Terms like "revere", "venerate", "consider holy", "hold sacred", or so on, are more accurate for animistic cultures. And relatable: for example, many Christians consider holy water to be "holy", but they dont "worship" this water. Similarly, Daoists revere the five elemental motions, as fundamental forces, but dont "worship" these elements. If a specific animistic community is "worshiping" anyone, then it connotes some form of theistic traditions have developed in addition to the animistic traditions. Since Dark Sun clerics are nontheistic, "revere" conveys the flavor better. That said, the sorcerer-kings are a kind of divine-king, analogous to "worshiping" Caesar as a god to some degree. (Traditionally, Romans believed the Caesar family ascended to heaven after death, thus became immortal gods posthumously. Egyptologists still debate what sense the Pharaoh was understood to be a god.) So, the Dark Sun setting might have a sorcerer-king demand to be worshiped as a "god". The dragons appear to have eternal youth with an indefinite lifespan, so at least in this sense they are "immortals". In sum, use "revere" for animistic concepts. Use "worship" for theistic gods.
My fourth thought, Dark Sun Druids are animistic. They consider significant landscape features to be outdoor sacred spaces. Features include sacred wellsprings (of healing waters?), and extend to holy mountains, and perhaps sacred ancestral burial mounds, and other notable topography. It might well be, the wellspring itself is a conscious being with psionic abilities. But the flavor focuses on the other "spirits" that "guard" the wellspring. In an animistic context, a "spirit" is more like a dream about something. This something is always concrete. For example, if there are birds around the wellspring, the spirit of the birds is actually the literal physical birds themselves, even if a Druid might communicate with these actual birds by means of a spirit journey during a trance. Likewise, when a person dies, the breath leaves the body as literal wind − a conscious breeze! − and the corpse turns into dust − conscious dirt. The psionic consciousness of the formerly living person is still present, but now rather than being a body, the person has shapeshifted into the elements of earth and air. For animism, things are always literal, never poetic, despite trance journeys sometimes feeling dreamlike. As a rule, whatever is meaningfully "significant" will also have a more palpable consciousness − thus stronger psionic influence. Animism is entirely this-worldly. Thus the "Gray" if a separate other-worldly plane is non-animistic. As such, it might be better to explain the Gray as an aspect of this material world, being a psionic matrix of the internetting minds of this world. In other words, the Gray is NOT a separate plane. Rather it is a feature of this world, albeit a subtle feature. The Gray is more like a virtual "augmented reality" that overlays the material world, that psionically sensitive persons can detect and observe.