A religion may have saints, prophets, and other religious leaders who impacted the faith, sometimes negatively with a betrayal of an oath or the god and teachings. Perhaps they went too far in pushing an agenda and either gods or species turned on them. They could also have inspired brutal administration of policies that result in harsh treatments. On the more positive side are those who inspire people. Create a few names, decide when they lived and died, and what they did to earn their esteem; just have them embody what the religion stands for, or part of it, with a significant deed or years of adherence to the ideals. They are a symbol. Focus on ones our characters reference or who will appear in our work.
A religion can have sects that disagree about interpretations of texts. Go easy on this if creating a pantheon due to the volume of work that could result. If we have two or more thoughts on how something could be done, use both, assigning ideas to sects. Each will oppose the other(s) and likely want them eradicated or drawn “into the fold,” making this a good source of tension. This is especially helpful if our world has only one god, because one religion causes little tension, whereas multiple interpretations and doctrines cause conflict. Create a few incidents in the past, ones that solidify dislike of the other(s) and exemplify and justify the animosity.
This religion, its followers, and its clergy have relationships with settlements, sovereign powers, species, and other groups, whether that’s another religion or the military. This can be a lot to work out, and most of that can be decided on a case-by-case basis when we need it, not in advance. Species are different and should be fleshed out in our overview of this religion. One, like humans, might be drawn to this faith while another tends to be repulsed by it. To decide this, we’ll need to have a solid understanding of the species and its outlook, which includes areas of turmoil that a religion can calm. This might be one of the last things we decide for this faith because a comprehensive sense is needed to form this association.
Does the religion feel that members of a species are in particular need of their teachings? Are they known for targeting elves, for example? Elves would likely know this and possibly feel irritation or outright hostility if this is considered condescending. Exasperation with a religion is a common feeling, while bonding with those of a different one is another. Decide what’s typical of a species, using their outlook, the religion’s, and the story needs as a guide.