If asked whether I am spiritual or religious, I answer yes. I am spiritual where spirituality exults in the supremacy of Jesus as God over all. I am religious where religion emphasizes Jesus’ way, truth, and life as the be-all and end-all of human pursuit and experience before God.
I answer this way because I am also evangelical. Most evangelicals shy away from both designations unhinged from gospel doctrine. Even though Christianity is a world religion, evangelicals ambivalence with “religion/religious” as self-referential goes back 80 years or so to the fundamentalist-modernist controversies of the twentieth century. As the Christian consensus of early eras began to atrophy in the American psyche, adjectives attempted greater precision—Bible-believing, soul-winning, creedal, socially-conscientious—but accomplished pigeonholing too. More recently, evangelicals have gone to calling ourselves “gospel-centered” in preference to religious.
Our cognitive dissonance with religion/religious is largely due to our experience of redemption. Because Jesus justifies us before God by grace through faith alone, according to His merits and works, apart from ours, we distance ourselves from what Paul called “self-made religion” (Col. 2:23)—systems and strategies whereby I try to earn my way with God by impressing Him with my good efforts or appeasing Him with Sunday rituals while living autonomously. This is what most evangelicals have come to regard as religion.
The word also has positive usage in Scripture (like James 1:27). But I still balk a little when someone refers to me as religious. I can’t help it given my pedigree, even though I know we evangelicals overreact to the term. “Religion” is a catch-all term in popular usage with connotations we can and cannot affirm. “Spiritual” even more so, although that too can be a perfectly fine word biblically (e.g. 1 Cor. 2:14-16 and Gal. 6:1). But many of the people who consider themselves “spiritual” are essentially just redrawing constellations according to their own “metaphysical dream of the world” (Richard Weaver). The phenomenon of “spiritual, not religious” was critiqued well here: http://religion.blogs.cnn.com/2012/09/29/my-take-im-spiritual-not-religious-is-a-cop-out/.