I get increasingly impatient with the way people talk about ‘religion’, as though all religion was essentially the same. It is such a broad category, and different forms of religion are so different from one another, that it really makes no sense to talk about ‘religion’ at all.
Religion seems to have changed massively in the course of evolution. There is a widespread misconception, popularised by the so-called ‘cognitive science of religion’, that religion has always been primarily a matter of beliefs about gods. But I think that is clearly wrong. Religion started with physical practices like trance dancing before it became a matter of belief, as people like the Oxford evolutionary psychologist, Robin Dunbar, have emphasised. There is still a big difference between forms of religion that, at core, are about practice and those that are about belief.
What people mean by ‘religion’ has also changed hugely over time. The modern way of contrasting religion with secularity is probably only 150-200 years old. ‘Religion’ has also come to be thought of as a private matter, though that used not to be the case. For mediaeval thinkers like Aquinas, your ‘religio’ was just your lifestyle, a matter of correct practice, not anything specifically ‘religious’ in the modern sense at all. ‘Religiosity’ has come become a negative concept, though it used to be a positive one. These quick examples indicate a massive shift in what people mean by ‘religion’.
The so-called ‘world religions’ are also very different from one another. I think one of the most important differences is that some so-called religions are largely a matter of cultural and ethnic identity; others are elective in the sense that you opt in or out of them as a matter of choice. Christianity is probably the most elective of the world religions, though Western Buddhism is similar. Islam, Hinduism and Judaism are much more a matter of cultural identity. There is much antipathy to religion, though Buddhism often escapes being a focus of hostility.
Religious people also differ hugely in open-mindedness, one of the big five personality factors. Conservative religious people are low on open-mindedness, and seem to almost believe in the importance of not being open-minded. Liberal or experiential forms of religion, in contrast, make a virtue of open-mindedness. We have here two approaches to religion that differ from non-religious people in opposite directions. That surely shows that it is quite hopeless to try to establish how religious people differ from non-religious people. Religious people differ too much among themselves for that to be possible.
I could go on, but I hope I have said enough to illustrate how diverse religion is. It seems to me one of the key weaknesses in much academic writing about religion that it doesn’t fully grasp this. When I was recently asked to comment on the set of proposals for the future study of religion published in Religion, Brain and Behavior, I felt this was the main problem I wanted to highlight. See: http://www.tandfonline.com/doi/abs/10.1080/2153599X.2016.1249930?src=recsys&journalCode=rrbb20
A final complexity is that some religious people are actually against ‘religion’. In many ways, that is true of great religious leaders like Jesus. The Buddha also did not see himself as teaching a ‘religion’, though there are later forms of Buddhism that are more religious. In the 20th century there are religious leaders like the great Dietrich Bonhoeffer who, when imprisoned by the Nazis, write movingly about his vision of a religionless Christianity. It is a vision with which I have a lot of sympathy.