More than 80 percent of the world subscribes to some “religion”; one might expect the word to have a straightforward meaning. Yet there is no universally accepted definition of the term religion. Religions take fundamentally different approaches to truth, Scripture, behavior, and reason. The same is true of a host of other concepts, such as meaning, experience, tradition, tolerance, unity, conformity, authority, deity, doctrine, salvation, morality, sexuality, family, death, and humanity. Some cultures view religion entirely separately from individuals or society. Others don’t distinguish those concepts enough to consider “religion” a meaningful category.

A general definition of religion can be distilled from these widely varied experiences as “a system connected to spiritual and/or supernatural components that uniquely impacts the adherent’s worldview, behavior, belief, culture, morality, and approach to certain writings, persons, or places.” Even simplified, that’s quite a mouthful—and a mind-full. The lines between religion and culture or philosophy or tradition or myth are not easily drawn.

Religion-as-a-category is hard to define, but specific examples are clearer. Most people connect to something easily identified as a religious belief. These systems self-identify as religions and exist far from the fuzzy edges of definitions. Examples are Christianity, Judaism, Islam, Hinduism, Buddhism, and Sikhism. These are straightforwardly called “religions” and come with all the expected features—over which they deeply disagree.

As with other broad terms, religion takes on narrower meaning in certain contexts. A common instance focuses on behavior. In that usage, references to “religion” emphasize actions or attitudes: rituals, prayers, behaviors, or confessions of doctrinal belief. Or, greatly simplified, “rules and rituals.” A person who often prays and attends church would be seen as “practicing religion.” In contrast, someone who never prays or attends church would be considered “non-practicing,” even if he claimed that faith.

The Bible addresses the concept of religion, but not as often or directly as one might expect. Clear references are almost exclusively found in the New Testament. This reflects a difficulty in defining religion; the ancient world intertwined spirituality, identity, and culture such that independently defining religion would have been redundant. Greek and Roman philosophy, followed by Christianity, contributed to the modern theme we now describe as religious belief.

Biblical references to “religion” typically use the narrow focus on behavior. In James 1:27, for example, the word religion references acts of worship—that is, the expression of faith: “Religion that God our Father accepts as pure and faultless is this: to look after orphans and widows in their distress and to keep oneself from being polluted by the world.” Note in his description the lack of commonly accepted “tools” of religion: James does not mention religious objects, holy days, memorized liturgies, or special hand gestures. Pure religion involves helping others in distress and maintaining personal holiness. Jesus frequently criticized hollow, hypocritical behavior not rooted in sincere faith (Matthew 5:27–28; 7:21–23; Mark 7:9–13; Luke 11:42–44).

Scripture also explicitly contrasts the idea of religion as a practice with faith-in-and-of-itself. Speaking to non-believers, Paul noted altars to manifold deities and said the people were “very religious” (Acts 17:21–23). James says religion not producing self-control is “worthless” (James 1:26).

A parallel to how Scripture views terms such as religion or religious would be terms such as politics and political. Politics are important, in their own way, since “politics” is how a culture translates moral and ethical beliefs into laws and government. A person can be “political” while maintaining a sense that political parties, laws, and elected officials are not literally the most...