When I studied comparative religion in the 80s it was a commonly accepted idea that there were many religions: Buddhism, Christianity, Judaism, Islam, Hinduism, and various smaller ones — perhaps new religions, pagan religions, small nature religions such as Shinto. This idea was developed as a response to the colonialist and triumphalist idea that there is the one true faith and those who aren’t its adherents dwell in darkness. But it leads to other problems. How do we count them? Is Christianity a form of Judaism or it’s own thing, and who gets to say — Jews or Christians? Is the Aristotelian Maimonides a Jew or a Greek?
More fundamentally if there are these free-standing important things called religions, it seems we must pick one — or perhaps none. And how could we do that? Do we accept the one we are born into, and therefore feel a gulf from our neighbor who was born into a different one? Are we of different religions condemned to clash? Must we fear the human born into a different religion, who bows strangely, eats strangely, and commits inexplicable violence for an impossible-to-understand conception of God?
A better way to look at it might be to view acting religiously or experiencing life religiously as something we all share, or can share, much as acting musically or appreciating music is something we all have the potential to share. Sure there are traditions of different religious practices, and concepts, and images, just are there are traditions of musical scales and musical instruments. But an individual or a group is free to mix and match. People can violently reject some aspect of the musical tradition, as folk music fans rejected Dylan’s use of the electric guitar, but they do not have to. It is more natural or at least as natural to observe a particular religious use of language, or image, or social interaction and pick it up.
We need not view “belonging to a religion” as the fundamental category any more than we view “being a guitarist” as a fundamental category. The fan of the piano may pick up the guitar. And the fan of the jazz piano and the jazz guitar may discover they have more in common than either does with the afficionado of the classical guitar or the flamenco guitar.