For example, a lot of people in the world believe in reincarnation. This is a belief that will never be proved or disproved. At least, nobody has ever suggested a way of proving or disproving it. Like all religious beliefs it rests on the idea of faith.
You could ask questions like, do single-celled organisms get reincarnated? Do viruses? Do the individual living cells that make up multi-cellular organisms like humans all get reincarnated? If not, why not?
You might feel that the theory is starting to fall apart under the onslaught of such detailed interrogation. Or you may reject the questions as invalid, although they seem perfectly reasonable to me.
You can believe in reincarnation if you want or not believe it. I don’t care. It’s not a belief you can prove or disprove. So paradoxically, although this is a belief built on faith, it’s not something you can have any faith in. And yet people build their lives around this kind of belief.
In ancient Egypt, people believed they needed to learn magical spells to ensure their safe passage through the afterlife. If they didn’t learn the spells properly they would be eaten by demons. That’s a pretty important belief. But it was never proved or disproved. It simply went out of fashion. It was vitally important to the people who believed it, but not to anyone else.
That’s the thing about this kind of belief. You can believe it or not. It doesn’t make any difference, at least not in this world. And as for some “other world”? Who knows? Nobody. So why believe in a religion at all? Or why not believe in all of them? It seems so arbitrary.