You could conceive spirituality as the study of the immeasurable, of the qualitative. But that's very different from the way we typically use the word. A spiritual person, in the popular conception, is somebody who's kind of aloof from the world, introspective, meditating, communing with non-material beings. That's the spiritual realm, and we elevate it above the material realm. What's more worthy, what's more admirable? Who's the one who has done this hard work on the self, and has done a lot of "practice"? That's the spiritual person.