The religious vs. spiritual debate is perhaps a modern one. I suspect that the ancients and medievals would tell us that we are making much ado about nada. Institutional religions, of course, would say that sprituality exists within them; they could also point to explicit spirituality programs. Christianity, for example, goes to the extent of proclaiming the work of the Holy Spirit, a person or manifestation of God, in the Church as well as in the individual members.
In short, I think the distinction between a religious and a spiritual person has been overdrawn, and has perhaps been fueled by prejudice against “the other side.” When a person says “I am religious,” it can be taken to mean that that person is a spiritual person, and vice versa. People without an agenda do not fret so about any proclaimed distinction. That is, I suspect that in modern parlance, the two terms blur together even if some have a vested interest in seeing that they are pried apart. I think historically this has been the case, though for people in the profession spirituality has referred to something within the religion. To say that now such spirituality no longer needs the roof of an institution is not to say that being spiritual is not religious. If there is a distinction to be made, it could be that spirituality refers to one’s inner feeling or experience while religion refers to the sphere or domain (e.g., the field) in which it is taking place (i.e., institutional or not). By analogy, politics goes on in the political realm. Or, politics is an activity in the civic domain. How much difference is there between politics and civics? The particular polity, ecclesiastical or civic, does not seem all that relevant here.
Also, I think the distinction between following the beliefs promulgated by an organized religion versus one’s own idiosyncratic beliefs is overdrawn as well. With few exceptions, I bet that most people who identify themselves with a particular organized religion have their own take, or interpretation, hence the “collective vs. idiosyncratic” distinction is, I would argue, overdrawn. Even people who view their religious beliefs as idiosyncratic must surely have imbibed to some extent collective beliefs, even if unconsciously. Finally, the quality of the beliefs–and more importantly the faith (which is not necessarily cognitive)–is more important, I would argue, than whether they are shared in common or idiosyncratic. That quality, I submit, is <em>sui generis</em> in the sense that a faith, whether you want to call it religious or spiritual, is oriented beyond the limits of our world. Besides being of value in itself, this transcendent nature of religious faith or spirituality means that we, ourselves, cannot be the focal object. In fact, the object cannot be known or perceived in itself; only its immanence can be felt. To sense the real in our world even as one grasps or is oriented to the transcendent is, I submit for your consideration, the core of religious spirituality or spiritual religion. Put another way, a person who feels herself spiritual and a person who feels himself religious are much more alike in these respects than they are to a person who really doesn’t give a damn about either being religious or spiritual. A person can be spiritual or religious and yet not take so seriously the sort of pretended minute distinctions that have historically sparked war. I suspect that if one really is spiritual or religious, he or she would naturally transcend meaningless distinctions, which would otherwise be felt as an inconvenient distraction. The implication regarding those who insist that we make the distinction is…well, you can connect the dots here.