Religion is a huge part of life for most of the world’s people. Almost all of the world’s 6.5 billion people belong to one or more of the major religions (along with a few smaller ones like Rastafarianism and Scientology). Many of us take it for granted that religion is an important part of their lives. But what exactly is it? How do we understand its importance in our world? And what is the best way to measure it?

Throughout history the concept of religion has been shaped and reshaped. Once a word for scrupulous devotion, it became the name of an abstract type of social practice that encompasses many different types of religious activity and beliefs. As this happened, the concept’s sense grew and shifted, and its definition arose in response. In the past, scholars of religion have typically used a substantive or a functional definition. Each of these approaches has advantages and disadvantages.

Substantive definitions of religion focus on the presence of belief in a distinctive kind of reality. But this approach has the danger of being too broad and of missing faith traditions that emphasize the immanence of God or of nature, such as certain forms of Buddhism or Hinduism. Similarly, when a functional definition of religion is used, it may exclude some practices and beliefs that generate community cohesion or give meaning to a person’s existence, such as secularism or consumerism.

These definitions are both problematic, but they have been helpful in shaping research on religion. They have made it clear that if religion is to be studied, it is necessary to look at the various ways that it affects a person’s behavior and his or her attitudes and values. This approach has helped to make it possible to study religion in relation to other aspects of human life, such as political systems and business organizations.

It has also prompted scholars to shift attention from mental states that are hidden from view to visible and observable institutions and disciplinary practices. In this shift, scholars have sought to overcome the problem that many of these mental state-based theories of religion face: that they tend to ascribe intentionality and control to invisible, subjective states rather than to visible institutional structures.

While the debates around the definition of religion continue, the fact remains that most of us find something in religion that gives our lives meaning and purpose. It is a source of spiritual and moral guidance that teaches us to choose good over evil, right over wrong, justice over injustice, truth over lies, and so on. It is a source of the power to persevere in the face of death and to find comfort in loss.

As the world’s varying religions have developed and changed over time, they have also become an integral part of the human experience. They have provided inspiration for the arts and architecture, agriculture, music and dance, drama and poetry, explorations of the cosmos that issued into natural science, and more.