This video is long, but informative and thoughtful.
We live in a very secular world today. Many people, even those that are religious, think of church as something you go to once a week. It is rare for it to influence the everyday activities of people. I know this because I was raised in a religion where I was expected to think of everyday activities religiously. I was considered weird for doing so, even by other religious people that considered themselves devout. This is very different from how religion has been practiced for most of history. There are very few things that would not have been thought of religiously. The government was religious, medicine was religious, slavery was religious, even your food was religious. In polytheistic religions, many gods were identified with specific locations, such as mountains, rivers, or towns. In my understanding, if you asked a viking why they believed in Thor, they would be as confused as if you asked them why they believed in lightning.
People did talk with the gods (prayer). People gave things to the gods (votive offerings). Many people saw things they believed were gods (specific locations and visions). That is not to say Zeus provably existed. But that is to say the effect religion had on people of the past was as important as if Zeus was provably real. When people in the middle ages poured wine on wounds, they didn’t know why it helped prevent infections. They just knew that it worked and had a different explanation than the scientific one we have today. Magic was real. We just call magic that works science.
I do think religion in a fantasy world would be different from the real world, but moreso because of the mechanics of magic and divinity than the “reality” of it. Here’s is a single example for how magic might effect how people view death.
Depending on how common high level spellcasters are, I think it would influence how people think of death. If spellcasters that can cast Resurrection and True Resurrection are extremely rare, but those that can cast Raise Dead are decently common, I think people wouldn’t consider someone to be truly dead until after 10 days have past. These 10 days might be viewed as a time when the body stopped working for whatever reason, but the spirit remains inside it. People would develop rituals to preserve these bodies, talk to the spirit inside, and try to keep it from moving on. Structures would be constructed where bodies could be kept cool in a location safe from scavengers. Bards, Clerics, and Paladins all can cast Raise Dead. They would become important figures in fantasy societies, similar to doctors. This would be very different in a setting where Revivify is the highest level readily-available resurrection spell or one where True Resurrection is common.
In other words, magic wouldn’t just become science. In a game like D&D, where magic is reliable and can be taught reliably (Wizards, Bards, Clerics), magic is science.
Gods would be worshipped based on their effectiveness, consistency, and closeness. No one’s going to worship the God of Numbers, even if they were provably real, because most people aren’t mathematicians and don’t need what they’re selling. But you would worship the God of Doorknobs if that was the only way you could reliably open doors.
