Nothing has been more polarizing in conversations than faith — or, more often, conflicts between members of different religions. I will try to unite everyone now (or make everyone just as angry). I believe we are simply thinking about faith narrowly, which causes all the disagreement.
First, let me identify the most fundamental concept of a belief: a statement that an individual makes that that individual considers to be true (and as such, uses as a basis of decision-making), a conclusion about reality as we perceive it. Beliefs don’t have to beaxiomatic (I can believe in something that someone else could prove to be derived from another, more fundamental truth) or even consistent (since we don’t mechanistically apply our beliefs to our life, inconsistencies can persist without any day-to-day conflicts). We all have beliefs at a variety of levels — from a set of grand ones (“I believe that I will be reborn after I die”) to tiny ones (“I believe I deserved that cake”). Sometimes belief is thought of as a conclusion that can be understood or known (as opposed to one that one can only place hope in), but I’ll define is as the broader concept.
There are some concepts that derive from belief that will be useful here. Spirituality is a belief in the immaterial. What is immaterial changes over time (before the discovery of magnetism, the force with which two magnets attract each other could be seen as of spiritual origins); spirituality also takes many forms, from abstract (an invisible energy field that permeates every human being) to specific (ghosts). Faith is a set of beliefs internal to each person that deal with the unknowable.
Finally, religion is an institution that proposes a particular framework around faith.
Of all these concepts I think faith is the most interesting one. What is “the unknowable”? In my view it’s precisely the set of statements that no logical person will be able to confirm or refute. For example, “There is life after death” is unknowable — there is no logic that includes the axioms that define the words “life”, “death”, “existence”, and “afterness” that can prove the statement. “2 and 2 is 5″ is not unknowable, because a logical person can prove that given the definitions of “2″, “addition”, “equivalence” and “5″, the statement is false (interestingly, as Gödel showed, there exist statements that are undecidable so they could theoretically form a basis for someone’s faith).
A crucially important property of faith is that it’s personal, and, more importantly, one person’s faith cannot in any way be compared to another person’s faith. Specifically, one person’s religion cannot be superior to another person’s religion because religions are organized around the idea of faith, which is only applicable to a particular individual. Obviously, in reality religions as just institutions and so they employ a variety of devices — competitive differentiation (or, in the extreme, instilling hate of other religions) being one of them in their plight for survival, and there is nothing surprising about it unless a religion becomes too powerful (and just like institutions, monopolies can have a very negative effect) or becomes a device in the hands of, say, a government (in which case it’s likely abuse of power).
Faith is also universal. Everyone puts faith in something, because our observations very quickly lead us to the unknowable. We don’t have to go very far either — while you may believe in the current model of the Universe (it’s expanding and finite, by the way), it’s still a model and no logical person can prove it’s a complete model. Furthermore, as of today no logical person can tell why it’s that model and not any other model. It’s a common fallacy of many intelligent people to assume that a belief in the current model of the Universe (or even in the scientific method itself) has nothing to do with faith — after all, science cannot prove the model is right; it can only prove that it’s wrong.
In a way, then, we could create an equivalence of all systems of faith — they all serve the same purpose, they are incomparable, and they are universal. It doesn’t matter what a person’s faith is. They are all the same.
If people didn’t organize themselves in religions, there would be much less conflict since discussing one’s faith is harder and looks more like trying to compare apples to oranges. However, just like people organize themselves in nations, they will organize themselves in religions because of strong community-based synergies (mostly good ones — a strong support network, a strong shared moral context making the society safer as a whole, institutional memory). I wouldn’t be surprised, however, in the age of the rising individualism made possible through the vast improvements in efficiency (I wouldn’t be surprised if we could create our own religion online) if more people converted away from their religions and into the more fundamental (and thus personalizable) faith systems.