Written in 1985 by Rodney Stark and William Sims Bainbridge, The Future of Religion was controversial book written in a era when many religious scholars were of the belief that religion would soon be homogenized into a single, universal belief system. Through analyzing the various religions in existence at that time, Stark and Bainbridge were able to show that this was far from the case, and that diversity among religions was greater than ever.
What makes The Future of Religion stand out was the classification system Stark and Bainbridge used to describe the various religions they encountered, a system which is still widely used today. They divided the majority of religions into three groups: churches, sects and cults, and based the division on the amount of tension that existed between the religion and society. The terms "church", "sect", and "cult" had been used before, of course, but Stark and Bainbridge took it upon themselves to further define and extrapolate the terms
A church according to Stark and Bainbridge, denotes a religion at the lower end of the tension spectrum between itself and the society surrounding it. Tension denotes a deviation from the beliefs and values held by that society. Therefore, a religion fully recognized and embraced by a community could be classified as a church. Churches are often the parent religions of sects.
A sect most often results from a group of believers who have divided, or splintered from a parent church. Unlike cults, sects represent a "return" to traditional beliefs from which the members of the sect believe the parent church has begun to deviate. Sects lie within the middle regions of the tension spectrum, though there is some overlap with the more radical churches. Many Christian denominations (particularly the more recent ones), can be classified as sects.
Cults are the group which held the most fascination to Stark and Bainbridge, who dealt with them at length. Cults represent either a cultural importation or some form of religious innovation and fall towards the absolute extreme on the tension scale. Stark and Bainbridge recognized many more cults than those usually recognized as religions, subdividing them into audience cults, client cults, and cult movements.
Audience cults, at least at time of Stark and Bainbridge's research, were the largest and most diverse type of cult. They have very small followings, if any at all, and are most often seen in the form of traveling seminars or conventions in which many cults participate. Attendees at such conventions can attend seminars and purchase books and materials espousing many different viewpoints and belief systems.
Client cults are the second largest type of cult and probably the least likely to be recognized as such. Their practices take the form of products and services which can be purchased for a fee or donation. Followers take the form of "clients" who buy the viewpoint as well as the service itself. Several well-known client cults eventually grew to become cult movements, notably Scientology and The Process.
Cult movements are what most people think of when they hear the term cult. Due to their position on the extremely high end of the tension scale, their large followings have been known to try to separate themselves from the outside world by living in compounds and communal living quarters. Others affect complete changes in lifestyle or even give up their worldly possessions to continue to afford the services offered by the cult.
One phenomenon remarked upon by Stark and Bainbridge is the transition of religions over time. Few churches actually start out as churches, but as cults or sects, and gradually evolve into churches as the population begins to consist of followers who were born into the religion rather than joining it willingly. Some of these followers might then splinter off, forming sects, or join cults, thus starting the process over again.