We’ve seen a long-run decline in prayer, church attendance, identification with particular religions, and belief in God or the importance of religion. I tend to attribute such trends to increasing wealth. Adam Gopnik agrees:
What if, though, the whole battle of ayes and nays had never been subject to anything, really, except a simple rule of economic development? Perhaps the small waves of ideas and even moods are just bubbles on the one great big wave of increasing prosperity. It may be that the materialist explanation of the triumph of materialism is the one that counts. … The daily miseries of the Age of Faith scarcely exist in our Western Age of Fatuity. The horrors of normal life in times past, enumerated, are now almost inconceivable: women died in agony in childbirth, and their babies died, too; operations were performed without anesthesia… . If God became the opiate of the many, it was because so many were in need of a drug. As incomes go up, steeples come down. … Happiness arrives and God gets gone. “Happiness!” the Super-Naturalist cries. “Surely not just the animal happiness of more stuff!” But by happiness we need mean only less of pain. You don’t really have to pursue happiness; it is a subtractive quality. Anyone who has had a bad headache or a kidney stone or a toothache, and then hasn’t had it, knows what happiness is. The world had a toothache and a headache and a kidney stone for millennia. Not having them any longer is a very nice feeling. On much of the planet, we need no longer hold an invisible hand or bite an invisible bullet to get by. (more)
Even so, almost everyone is religious to some degree:
Most [who say they don't believe in God] believe in something like what the Super-Naturalists would call faith—they search for transcendence and epiphany, practice some ritual, live some rite. True rationalists are as rare in life as actual deconstructionists are in university English departments, or true bisexuals in gay bars. In a lifetime spent in hotbeds of secularism, I have known perhaps two thoroughgoing rationalists—people who actually tried to eliminate intuition and navigate life by reasoning about it—and countless humanists, in Comte’s sense, people who don’t go in for God but are enthusiasts for transcendent meaning, for sacred pantheons and private chapels. They have some syncretic mixture of rituals: they polish menorahs or decorate Christmas trees, meditate upon the great beyond, say a silent prayer, light candles to the darkness. They talk without difficulty of souls and weapons of the spirit, and go to midnight Mass on Christmas Eve to hear the Gloria, and though they leave early, they leave fulfilled. You will know them by their faces; they are the weepy ones in the rear.
So religion will remain a big influence on the world even if we keep getting richer. And if wealth per person falls a lot, as I forecast, religion may well resurge to near its former levels of importance.