Some religious orders forbid the use of force or carrying weapons while others have armed and trained warriors. A decision is easy for a god of war or peace, though the latter could acknowledge that people must defend themselves and that peace can be achieved through might, so we can once again put a spin on our invention. If we go with a less obvious rationale like this, we can state why with exposition or a scene like this one:
Kier disdainfully glared at the priest, hefting his sword. “Stand aside or be cut down.”
The priest patted the blade slung at his waist. “My goddess may treasure peace, but she’s not foolish enough to simply turn the other cheek. I know how to use this.”
“You had better, or you will meet her soon enough.” Kier advanced only to find the priest swiftly raising a blade that clanged against his twice before his fell to the floor.
For each religion we invent, a sense of the god’s impact (through clergy) on the world and our story can guide our decisions. Do we want priests to be passive and easily bossed around or do we want more strength of behavior like the one depicted just now? Decide what feels right.
When weapons are forbidden, there’s often a rationale, which can be a deep part of a religion’s views. With Christianity, Jesus taught about turning the other cheek, and this humility is an inherent part of every religion that is based on his teachings. With our invented religion, do we have a rationale we can use to justify a lack of violence? A god of greed might want followers to fight to gain or keep what they have, or at least see it as a practical necessity. But does a goddess of the forest feel this way? Maybe not for a long time, but if species begins decimating woodland like we’ve done on Earth, and all manner of non-violence has not inhibited the destruction, perhaps a change of approach is in order. Either way, don’t be afraid to challenge perceptions and expectations, which on Earth lead many to assume priests are defenseless wimps.
We should also decide if priests are to accompany warriors, whether this is for war or smaller outings. This may be sanctioned, or the clergy may find themselves in this position against their will, such as trying to save a wounded soldier only to find himself and allies fighting for their own lives. Are priests members of the armed forces and what rank do they have? It is presumably not every religion, so which ones gets this role? They sometimes must also administer last rites to the dead and dying.
If we’ve decided they use weapons or wear armor, we should specify what they are expected to have…
We should consider the effect weapons have on victims when deciding what priests are likely to use. A religion might forbid the spilling of blood and therefore suggest blunt weapons like the staff or mace. These still cause bleeding, of course, but it tends toward being internal. Blood is not only a symbol of life but also carries diseases, so whether it’s symbolic or a practical matter, this viewpoint can arise. Gods of war or death might prefer its spilling and allow especially destructive weapons like hollow-point bullets. Technology allows for weapons that kill in other ways, such as radiation. Light sabers or similar laser-like weapons cauterize wounds and prevent bleeding.
Consider whether suffering is something they want to minimize or maximize in victims. A faith might promote a swift death if it’s to happen at all and prefer bladed weapons (blood loss kills in minutes verses hours or even days). Others might prefer subduing someone and train people in martial arts. Such a tactic might leave the practitioner relatively defenseless against better armed and armored opponents.
Priests are only likely to wear armor when sent into combat on purpose, just like everyone else. For everyday living, local hostility levels will determine the feasibility of wearing light protection. What we want to decide is, if they’re armored, what is it? If there’s a lightweight chainmail, this can be worn under robes. Leather is another option, but even knights only rarely employ plate armor, so this is less likely. In SF, we might have technological armor akin to Kevlar, and we can invent these to be light and slim. These can also absorb or resist magical, godly, or technological power (like radiation).
Decide what sorts of forces they’re likely to encounter because this is what will determine the armor choice. Is there an aspect of this religion that informs the choice? For example, if leather is made from an animal that they consider unclean or sacred, then this is ruled out. If metal somehow interferes with communing with a god, so much for chain mail and the like. Armor might even be considered a barrier to being reunited with their god (through death) and therefore be frowned upon. Being creative with a choice makes this more entertaining for us and audiences. Otherwise, keep it simple.