Okay I got two tags asking to post my issues with how people worldbuild religion, which is enough, so. Here's my Personal Opinion overview of major pitfalls in how people handle religion in worldbuilding.
(Note that this is again tailored towards non-industrial/pre-modern era/general fantasy/etc settings)
FUNDAMENTAL ISSUES:
-Kneejerk assumptions that any religious beliefs you donāt personally understand, or that differ substantially from your own, or that are superficially irrational given what you (a person who has near-complete access to all accumulated human knowledge at your fingertips) know about how the world physically works, are a result of people just being Stupid. Often manifested as Smart characters just de-facto being quasi-atheists (or otherwise having beliefs closer to the author's own) while it's mainly the Dumb People that actually adhere to their culture's religion. If you're operating from that standpoint you aren't equipped to write religion well, don't have more than a basic understanding of how religion/religious thought Works, and don't have anything particularly meaningful to say About religion (INCLUDING criticism).
-In relation to that, an underlying assumption that religions are ultimately just (flawed/failed) attempts at developing an empirical understanding of the world. That religion Only (or even just Predominantly) seeks to answer questions about physical reality that are not self-evident to human perception. Religion is the compounding of a cultureās entire subjective reality. It instructs on their morality and values, explains why they have the practices they do, why they live where they live, why people are who they are, why society is organized the way it is, etc. It is a part of broader knowledge systems. It is a mechanism of control that compels people to behave in ways that benefit group cohesion and may provide additional perceived consequences to violations of law and taboo, enforces social norms, and can be a mechanism for enforcing hegemonic structures. It creates and regulates community and group identity. It is a complete worldview that encompasses both subjectivity and hard material forces that shape a culture. And yes, it does include explanations for physical reality and for unknowns like "where does everything come from" "what happens to the consciousness after death" "what exactly is the sun", but the answers to these questions have functions beyond the mere explanatory.
Basically, if you're writing religion as basically a series of checklists of 'here's how they explain x and y and z' with some gods slapped onto it, you're not really writing religion.
If the sun is carried on a chariot, it's not Just because 'well a chariot is an object we know to be capable of carrying things across a great distance, which explains the sun's behavior'. A chariot might be a critical weapon of war, and may be only accessible to lords who can own horses. Warrior status might be illustrious, an ideal of masculinity, a venerable pursuit. They probably experience warfare frequently and see strength in conflict as vital for their continued existence. In this example, the sun being carried on a chariot can suggest that the god who drives it as a lordly and venerable authority figure, an ideal of masculinity, a protector of his people and destroyer of their enemies. Is he chasing something across the sky? patrolling against an enemy above or below, or patrolling his lands to watch over those beneath? is he on his way to do battle with a foe in the underworld each night? etc (and you can expand on A LOT from there). The solar chariot has symbolic meaning that reflects people's values and lived realities, it's not just explanatory.
I saw a video recently showing a little wind vortex that REALLY looks like some invisible little animal is skittering across rocky ground with comments going āohhh now I get why people believed in spiritsā and like. If wind spirits are experienced in this people's reality, they're going to be the wind Itself, or certain kinds of winds, or entities that can control the wind, or etc. They're probably going to be part of a greater schema of spirits existing throughout the natural world, and they're gonna be part of your lived reality whether you've actually seen a creepy vortex or not. Certainly some mythologies are contributed to by/describe sightings of rare natural phenomena, but it's not like someone once saw a tiny wind vortex and went "that looks like an invisible creature made of wind. There must be invisible wind creatures which I will henceforth call 'wind spirits'".
-Treating religion as this thing that is wholly separate from culture (very often due to being culturally Christian and raised semi-religious, wherein religion is consciously Experienced as a thing you go to a certain place to do at certain times). In the majority of cases across history, a religion is an Inseparable component of its associated culture(s). It may very often be tied to a specific ethnic identity. Small rituals are baked into daily routines. There may be religious elements in how food is harvested and prepared, what and how you eat, what you wear, how you interact with others, how you clean yourself and your spaces, how things are built, the language you use, etc. Thereās very often no divide between a āsecularā and āspiritualā world.
And critically, most of this will be VERY MUNDANE. Thereās a tendency to depict such expansive practices as if practitioners are in a constant state of religious fervor, and thatās not the case. Someone who needs to salute their householdās guardian deities every single time they pass through the door will probably be doing it with the same emotional intensity as someone making sure all their lights are off before they leave the house. Itās just a thing you do. If a ritual is something that you see or do on a regular basis, it's probably going to be pretty blasĆ© (even boring) for people who are still deeply vested in its importance.
IDK I see a lot where religious practice is handled as either "everyone smart thinks its stupid and is just bored out of their mind throughout any religious event (they're bored because There So Smart)" or "believers do every form of ritual with the same fervor you see at snake handling churches when the holy spirit's gotten into them" (either within the same religion to distinguish the Smart People from the Stupid People, or with the latter angle being a signifier of a Bad Evil religion that is either an attempt to epically own Christianity or is extremely racist).
-Lack of syncretism. No religious worldview (or any other cultural element for that matter) is going to develop in a vacuum without external influences. ANY sustained interaction between different groups of people is going to result in the exchange of language and ideas. Geographical neighbors with different practices will likely share religious elements (potentially both from shared cultural ancestry and from a history of interchange). The religions of occupying forces will often absorb some facets of the occupied. Gods from different pantheons may be adopted and adapted for political reasons. Converts (whether forced, coerced, or willing) will carry some of their previous practices or ideas into their new one, and this is likely to develop into a distinct form of practice (and maybe eventually its own religion) in cases of group conversion. A society that deems its religion supreme and is actively hostile towards others is still not immune to the transmission of ideas. Your religions should never feel like they exist in a bubble, and should bear marks of a long history of interactions with other peoples.
-Being 'too neat'. Every aspect of the religion feels a little too tidy, too planned, has too few redundancies, and thus doesn't feel Lived In. This one can be challenging no matter how thoughtful you are because like, you're trying to replicate a cultural artifact that has been lived in for generations by a large group of people and shifted and changed throughout that time, but you're one person actively Designing it over a period of like, months or years. I think a one way to help is to Not be precious with consistency in your writing, allow self-contradictions to occur naturally and then revisit and iterate on them. If these contradictions defy FUNDAMENTALS of the religion (ie this religion is squarely monotheistic but you've written in something that sure sounds like another, lesser deity), then see how you can work this contradiction back into the fold without wholly removing it. And then iterate from that. And also just don't be SO stuck on any one idea that you're unwilling to change course if it starts developing in a different direction.
This process will give you elements you can ascribe to religious syncretism, or can describe as some relic of an extinct practice, or can build a schism off of (therefore giving you more to work with! What interactions resulted in this syncretism, what do other religions with common descent from this extinct practice look like, how and why did this schism develop and who adheres to it), and results in something that feels messy and therefore Lived In.
-Focusing too much on writing cool mythology and big rituals and too little on writing how religion manifests in day to day life. Like, you need to be considering what the average practitioner actually Does. How does religion factor into daily routine, clothing, art, language, food, entertainment, etc? And your mythology should not just be Cool Stories, you should be thinking of what values are being communicated, what anxieties are being expressed, how it reflects lived conditions and social systems of the people who tell them. Even if a story isn't a parable that intends to teach a lesson, it will be communicating things like values and morality and reflecting cultural biases all the same.
MISC POINTS:
-Assumption that all religions expect or favor orthodoxy. In a LOT of cases, people don't care what you Think about the gods, they care about what you say and especially what you DO. There may be a partial/complete lack of cultural Giving A Shit if you don't actually Believe in the core deit(ies), or if you believe in others, so long as you adhere to the orthopraxy expected for your station. Please take orthopraxy into heavy consideration and have systems in which it is the primary expectation of adherents.
-Assumptions that every religion has the concept of blasphemy, or cares deeply about it, or otherwise has strong distinction between the sacred and the profane. (Also remember that No Matter What there will be people who blaspheme and joke and make light of their own religion and push the boundaries of what they're allowed to do).
-Just in general remember that a lot of worldviews will have No separation between a mundane and supernatural realm. The afterlife (or the locations of deities or etc) is often going to be somewhere that's Inaccessible but still a part of the tangible world- in the sky, under the ground, across the sea, far away over land, etc. The notion of a divine realm as basically another Dimension is pretty modern and a result of consensus understandings of reality shifting because, yeah, we've mapped the earth and know a lot about its atmosphere and core and there's not room for a physical afterlife-space there. But it follows the same pattern, locating these divine spaces Just out of reach by mortal means.
And also some afterlives/spirit worlds have no degree of separation whatsoever, spirits may be an active part of the landscape in which one lives. The dead may be immediately present and interactive, sometimes taking the form of fauna or flora, sometimes as invisible forces, sometimes remaining in their corpses, sometimes residing in spaces made for them, or a combination. This is usually going to entail strong obligations to the dead and a sense of a continuing relationship with them, as well as strong ties to one's land in part because your ancestors are There.
-Pantheons in which there is one god assigned to each major concept (and potentially nothing else). Like you have one sun god, one moon god, one war god, one agriculture god, one fertility god****, one hunting god, etc. Pantheon systems do not develop by people delineating each major facet of reality and assigning a god to it. They aren't that cut and dry, they tend to have 'redundancies' (and their makeup will VERY often include deities adopted from other belief systems). Any given deity will serve multiple purposes (that may not be not overtly related), and separate deities will have overlapping purposes.
-****Fertility gods specifically piss me off because no one who gets published seems to know what the fuck they are. It Tends to be written as "This is the sex god who is about making babies (Sex) and maybe like, romance, and she's a sexy woman with huge boobs I mean a real set of badonkers. Packin' some dobonhonkeros. Massive dohoonkabhankoloos". The reason fertility is SO important to most religions across history is that it's the bedrock for basic subsistence. You need fertile crops, fertile livestock, fertile land, fertile wildlife, ALONG with fertile humans for your society to survive and thrive. Most deities that can be described as 'fertility gods' will have a focus on subsistence rather than just sex (or sex at all). You won't often find a deity whose Exclusive importance is human fertility, and even if you do it's probably going to include a variety of aspects (ie marriage, love, safeguarding pregnancy, safeguarding childbirth, safeguarding children, etc).
Just as a rule if you're writing a pantheon for a society that practices agriculture, there probably should be Several deities with an agricultural fertility bent.
-Sacrificial killings being written as like 'blood for the blood god', just killing anything you can get your hands on to please a bloodthirsty deity. There's a lot of different philosophies and purposes to sacrifice (does it appease certain deities? is it necessary for the world's continuing function? does it ward off disasters? a combination? etc), but the key underlying factor is that it is a SACRIFICE. It is giving up something that is considered valuable, important, difficult to attain, etc to achieve a greater purpose. Even with very cushy sacrificial models like the Greco-Roman 'burning the parts that aren't preferred for eating as offerings and then eating all the good parts' (they did also do some full cremations/offerings into bodies of water and stuff but I digress), it's still Giving Something Up. On subsistence scales, cattle and sheep and etc are MUCH more valuable alive than dead (they continuously provide food and fertilizer and fuel and textiles), slaughtering it as an offering MEANS something in a society in which slaughter can be an economic/survival gamble for the average person.
Human sacrifice can be more complicated in terms of whether it's strictly 'giving something up' because a LOTTTTT of the time it's members of an out-group or otherwise people considered 'expendable' (though should be noted that not every ritual killing that gets called a 'human sacrifice' would be considered a sacrificial offering by those who perform it). It often has STRONG political functions. If members of an out-group are sacrificed, it's purpose is often (in part) intimidation and a show of power or superiority. It may have implications for the afterlife - ie, warriors whose captives are killed at their funerals to serve them in the afterlife, monarchs and nobility whose slaves/servants/potentially even Officials are killed with them to continue their service in the afterlife. And in cases where sacrificial killings can Potentially happen to members of the in-group, there's often a notion that this is a good death, will grant good status in the afterlife, will gain the favor of a certain deity, etc. All this is just to say that it's never just mindless violence for the sake of violence.
-Monotheism ONLY being represented by Abrahamic (if not specifically Christian) style gods. IE: deities that are creators/rulers/kings, who are personified and have personal relations to you on some level, are omnipotent/omniscient/omnipresent, etc. There's a lot of variety into how singular gods are conceptualized, and some adjacent forms of belief ie- monolatry (multiple gods are recognized but only one is venerated) or henotheism (there is one supreme god but the potential existence of others is not rejected). The deity might be conceptualized as the world, the universe, something beyond the universe that contains it within, something from which the universe emanates, etc. God may be a specific Part of the world- the sun/the land/the sky/etc. God may not be heavily personified, or interacted with directly. Monotheism also isn't exclusive with other forms of veneration, like you can have monotheistic-animist systems, or monotheism with ancestor veneration (in which case the dead may often be go-betweens for the people and the god), etc. Branch out.
-Contemporary-type atheism in pre-modern type settings. To be clear I think there have been people who've thought 'I don't think this deity actually exists' since Belief In Deities has been a thing, but atheism that Utterly rejects every aspect of a belief system/exists as a movement detached from any other philosophy is pretty modern (see: religion usually being deeply embedded into the very fabric of its culture). Your atheists doubting the existence of god(s) are VERY unlikely to just automatically disbelieve everything else that could be labeled 'supernatural' or 'spiritual' in their culture. And any large-scale practice that disavows deities or creator gods is Most Likely to be attached to a religion and/or a school of philosophy (see atheist philosophical schools in the Vedic period and rejection of creator gods in Buddhism and Jainism).
