Rival religions expend a great deal of effort in magnifying minor differences between them. Yet, the major world religions fulfill similar functions and endorse analogous codes of conduct. They may also provide similar emotional and practical advantages.
All religions are based on dualism, or the notion that there is a supernatural spiritual realm separate from -- and more powerful than -- the natural physical world of our senses. Moreover, all offer a pathway through which members may interact with the supernatural world, whether directly through prayer, or meditation, or taking psychoactive drugs, or indirectly through a priest or shaman.
Shamanism
In hunter-gatherer societies, religion focuses mainly on the services of a shaman who enters the spirit world and negotiates with the spirits perceived to control the movement of animals. This is important for hunting success. Spirits controlling the animals let them fall into snares, or show up in front of a hunting group. Other key religious concerns include health and fertility.
Farming is a much riskier occupation than hunting and gathering because success often rides on a single staple crop that can be destroyed by rain, or drought, or a pest. In my book Why Atheism Will Replace Religion, I argue that agricultural societies are more intensely religious than hunter gatherers were because they have so much more to worry about.
In modern societies, religiosity is correlated with a low quality of life. This association is very general and includes low life expectancy, lack of education, economic under development, exposure to epidemic diseases, and lack of social mobility.
In sub-Saharan Africa, for example, where each of these issues is salient, virtually everyone is religious. In Europe, though, the quality of life is much better and there are some countries such as Sweden, France, or the Netherlands where the majority of the population either say that they are not religious or that religion is not important to them. (The U.S. is still a comparatively religious country despite its wealth due to high income inequality that degrades the quality of life, as discussed in an earlier post).
Religious people seek supernatural redress for their many anxieties. If a farmer is concerned about heavy rain flattening his corn crop, he may pray for fine weather. That isn't going to protect his crop but it helps him to feel less anxiety.
The functional core of religion
World religions all help their members to cope with anxiety. That impression is strengthened by fairly recent evidence that religious rituals and prayer are psychologically calming and capable of reducing blood pressure.
Of course, one can always find opposing viewpoints. The New Atheists, including Sam Harris and the late Christopher Hitchens argue that religion frightens and manipulates individuals and tears entire societies apart via religious wars.
By thumbing their noses at religious institutions, such authors achieve a certain notoriety that promotes book sales. Yet, I feel their perspective lacks proper scientific objectivity.
The scientific goal is to understand religions -- not to judge them as the New Atheists do. Moreover, religious beliefs and practices are found in all societies. If religion were as destructive as the New Atheists claim, then they would long ago have been removed by natural selection instead of prospering.
World religions endorse much the same behavioral agenda emphasizing clean living, respect for others, hard work, and other habits that likely favor health and reproductive success. Religious institutions may thus provide practical benefits as well as psychological ones. So why is religion declining?
If religion was so useful, why is it in decline?
The most plausible explanation for the decline in religion in the most developed countries is that the quality of life is improving. There is less need of religion as a salve for psychic pain from the tragedy, disappointments, and misery, peculiar to life in a poor country.
At the same time, there is no scarcity of competing consumer products that help with emotional pain from tranquillizers, new age yoga and meditation, to sports, music and entertainment that insulate us from the anxieties of daily life.