Some striking mile markers appear on the road through young adulthood: leaving for college, getting the first job and apartment, starting a career, getting married—and, for many people today, walking away from the Christian faith.

A few years ago, shortly after college, I was in my studio apartment with a friend and fellow pastor's kid. After some small talk over dinner, he announced, "I'm not a Christian anymore. I don't know what happened. I just left it."

An image flashed into my mind from the last time I had seen him. It was at a Promise Keepers rally. I remembered watching him worship, eyes pinched shut with one slender arm skyward.

How did his family react to his decision? I asked. His eyes turned to the ground. "Growing up I had an uncle who wasn't a Christian, and we prayed for him all the time," he said wistfully. "I'm sure they pray for me like that."

About that time, I began encountering many other "leavers": a basketball buddy, a soft-spoken young woman from my church's worship team, a friend from youth group. In addition to the more vocal ex-Christians were a slew of others who had simply drifted away. Now that I'm in my early 30s, the stories of apostasy have slowed, but only slightly. Recently I learned that a former colleague in Christian publishing started a blog to share his "post-faith musings."

These anecdotes may be part of a larger trend. Among young adults in the U.S., sociologists are seeing a major shift taking place away from Christianity. A faithful response requires that we examine the exodus and ask ourselves some honest questions about why.

Sons of 'None'

Recent studies have brought the ...

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