"Jesus came to start a movement, not an institution," says Jim Henderson, coauthor of Jim & Casper Go to Church: Frank Conversations about Faith, Churches, and Well-Meaning Christians . "As far as I can see, He never intended for what we call 'church' to be in existence. The casual way we accept this thing called Christianity is such an insult to the basic story and message of Jesus. I can't spend the remaining years of my sorry life standing by, watching this, and going, 'Oh, well.' It's a huge historical mistake." Henderson is a self-described Jesus-follower, a man who is "overtly involved in trying to draw people into a relationship with Jesus." What's more, he says, he's a "spiritual anthropologist," a man interested in why Christians act the way they do and in getting them to reflect a bit. He stresses that he's not crying out, "Churches are stupid! Get out of church!" But he is curious as to why Joel Osteen's Lakewood megachurch in Houston makes its Sunday service into "showtime," where "the spotlight is all on Joel and his wife." He's curious because "I happen to know that they're helping a lot of people in that city, a lot of poor people. All I would say is, 'Put the story of the way Jesus is working through you in public, and give the preacher just three minutes to talk.'" In short: tone down the attraction and emphasize the mission. Shorter still: less show, more go.

Henderson got the idea of "holding up a mirror to churches and asking them if they like what they see." To that end, he started http://www.churchrater.com , a website that evaluates church services in much the same manner as this column: an account of the service and ratings for singing, preaching, and friendliness. He also found Matt Casper, an atheist willing to spend a summer church-hopping with him and giving his reactions to what he encountered. Those visits provided the material for Jim & Casper Go to Church .

Casper wasn't just any atheist. For starters, he was baptized Catholic and grew up following his mother from church to church -- she sang in the choir. (Two years ago, she became Catholic herself.) He also attended a Catholic university. Says Casper, "I think going to Catholic school was part of what started me down the road to losing my faith. My logical brain seized on the point -- 'Wait a second, you mean the first gospel wasn't written until 70 years after Jesus died, and it wasn't written by this guy named Mark? I don't trust my own memory from last week, and I'm supposed to trust three generations of stories being passed around as fact? I can't do it.'" Eventually, he looked inside and found that his worldview "definitely didn't line up with one that entails or requires a supernatural element."

Still, that backstory left its mark, and when Henderson met his man, he found that "Matt demonstrated a serious familiarity with the same message of Jesus that I'm familiar with. But" -- and this was what made him an ideal participant -- "he had a very limited exposure to the church scene -- Christian church culture." And, happily for Henderson, "he's not a militant atheist. He's not, 'Up with atheism!' the way a recent convert to Christianity would be about faith."

Perhaps most important, Henderson met Casper in the first place because Casper was friends with Jason, a man who runs a home church here in San Diego. Marvels Henderson, "Here are two guys who have a very close friendship, but it's crafted out of something other than their beliefs or nonbeliefs. We're living in a time of incredible polarization, and I'd just like to model two people getting along and talking. Normally, they wouldn't be talking -- they'd be arguing."

Henderson believes it's a conversation worth having. "If people who had never heard of Jesus wanted to see what Christians were most interested in," he writes, "they would probably start their search in some of the same churches we visited.... Unless we're willing to remove the handles from the front door of our churches and publicly say to outsiders, 'We don't care what you think,' the church must become more reflective and repentant about how outsiders perceive us."

In conversation, he elaborates: "Churches keep talking so damn much about trying to reach people, and they suck at it. They don't even say 'Hello' when you go into the building." Or, as the two found as they visited megachurches around the country, there are official greeters working the floor. This wasn't always the case; sometimes, they weren't greeted at all, and other times, they were greeted in what seemed a genuine fashion. Still, he wonders, "What does it say about the Christian community that we have to plan to have people say hello?"

Casper relates a story that didn't make it onto the page, one from a local megachurch. "After the service, they greeted me by saying, 'Hi, how are you? When did you come to Christ?' It's a massive assumption. And in some churches, I felt like an attractive girl in a bar full of drunken frat guys."

In the book, the informed atheist proves a tough critic, suspicious of polish and pizzazz, harsh on bigness and celebrity, impressed mostly by sincerity and accounts of good done for others here on earth. More often than not, Henderson lets Casper's comments go unchallenged; occasionally, he'll ask a clarifying question. He's not out to convert his man; he's out to understand him. "All innovation lies at the intersection of opposites," says Henderson. "For me to be paired up with somebody who basically thinks that what I believe is a fairy tale and not fight with him, but actually sit and listen and learn from him, creates a certain kind of creative tension."