What's the most popular religion in the world?

About two months ago, I came across this article on Ask Yahoo!. In addition to the response itself, there are a number of other useful links to pie graphs, timelines, etc. I can't decide what I find more extraordinary - (a) that there are 5.2 billion people who are religious or (b) that there are 1.1 billion people who are "non-religious" or (c) that less than one half of one percent of the population is atheist. Although figures vary for each country, of the 1.1 billion (16%) who self-identify as "non-religious", roughly half of them also answer "yes" when asked if they believe in God or a Higher Power. So, loosely speaking, 84% of the population is religious, 8% is non-religious but believes in God, 7.5% aren't sure whether God exists (agnostic), and 0.5% don't believe in God (atheist). That just seems amazing to me. What is it in us as human beings that causes so many of us (more than 9 out of every 10 people) to believe in something that we can't see or touch or directly interact with? Granted, I'm one of those 9 out of 10 people now but it was a hard-sought battle to get there.

The other thing I find fascinating about this data is that if 9 out of 10 people believe in God, why isn't the world a better place? For example, one out of every three people is Christian. As my philosophy professor put it in one of his lectures, "imagine the state of the world if 2 billion Christians were living lives transformed by prayer and love into lives of service and compassion. What would 2 billion Mother Teresa’s and Saint Francis’ bring about? Would it bring about heaven on earth? The Kingdom of God promised by Christ? As one pundit said, Christianity has not failed so much as it has not been tried." Obviously we need to draw a distinction between the teachings and beliefs of a particular religion and the (imperfect) people who practice that religion. But it is an interesting thought-experiment to consider what the world would be like if we all lived our beliefs every single day.