I am not a jurist obviously, but this week's US Supreme Court decision in the Hobby Lobby case is alternately being praised as the beginning of the restoration of "religious freedom" or condemned as the recommencement of "Christendom," of turning Margaret Atwood's ghastly apocalyptic tract The Handmaid's Tale into reality. But in any case, all the commentary has casually and carelessly and indeed thoughtlessly been using "religion" and its cognates as though there were some coherent meaning to that term and universal consensus about it. There is not. John Milbank's celebrated 1990 book Theology and Social Theory: Beyond Secular Reason famously opens with the ringing declaration "Once, there was no secular" and thus severely puts to the question our casual assumptions about what is "secular" and what "religious" or "spiritual," showing the recent political invention of these terms, their invariably tendentious political usage today, and their rise in our consciousness--something later done in Charles Taylor's massive tome, A Secular Age.
The person who, to my mind, has been the most helpful, building on Taylor and Milbank (and others) in showing just what incoherent, inconsistent, and often highly tendentious meanings we ascribe to "religious" and "secular" or "Church" and "state" is William Cavanaugh, as I discussed here in detail when reviewing his book Migrations of the Holy: God, State, and the Political Meaning of the Church. Equally valuable, though in a somewhat different direction, is his 2009 book The Myth of Religious Violence: Secular Ideology and the Roots of Modern Conflict, which really shows what a mess the term "religion" is and how little consensus there is about its meaning even among scholars.
All this is preface to a new book that continues and deepens the discussion: Brent Nongbri, Before Religion: A History of a Modern Concept (Yale UP), 288pp. Perhaps journalists and other lazy commentators might bestir themselves to read one or more of these books before continuing their ignorant usage of these terms.