Why is it that people who have been saved can never adequately explain the experience to those who haven't? We've all encountered born-again Christians who have talked about feeling aglow with love, bathed in a warmth that is not of this earth. To those of us who, by those Christians' standards, walk in darkness, it sounds a bit like wearing polar fleece all the time, and who wants to do that? Those who haven't been drawn by God's call are destined to be mystified by its appeal.

With her memoir "This Dark World: A Memoir of Salvation Found and Lost," Carolyn S. Briggs finally breaks the barrier. In the early '70s Briggs was 18, a new mother and newly married to a sweet but not particularly enterprising musician; she and her small family were living in a trailer park in Des Moines when she first discovered the word of God. As a youngster entranced by a smooth-talking local minister, she'd toyed a bit with the idea of accepting Jesus Christ as her personal Lord and savior. But as she huddled with her husband, Eric, reading Scripture from a paperback Bible she'd bought at Walgreen's for $11.95, the words began to mean something new to her. Before long she and Eric were dedicated members of a radical Christian religious community called Fountain of Joy, a fellowship that some called a cult, but that Briggs saw as a supportive, loving environment in which a community of people stuck together to study the word of God and strive to serve Him as best they could.

Fountain of Joy was something of a hippie church, led by a group of elders and consisting of about 40 families who lived by the Scriptures. Women could not be elders; the Bible stated that women should defer to men in all matters. So Carolyn and her women friends concentrated on raising their families and loving their husbands, all for the greater glory of God. They genuinely looked after one another, taking turns cleaning house or caring for the children if a woman took sick. In their eternally beaming selflessness, they'd even nurse one another's infants.

Briggs thrived on the support and acceptance she found at Fountain of Joy, but her enchantment with it -- and, more significantly, with God Himself -- didn't last forever. What makes "This Dark World" an exceptional book is that as clear-eyed as Briggs is about her experience (she was a deeply religious Christian for more than 20 years), she also fully understands the ways in which her religion benefited and enriched her. Anyone can reject true believers as mindless Bible thumpers, but Briggs never takes that route; her hard-earned sophistication about spiritual matters isn't hollow.

That's at least partly because Briggs comes clean about the doubts she had even in the years she was most fiercely devoted to her faith. She admits to feeling despair at seeing how much the other wives seemed to love their husbands, spiritually and physically. Briggs considered her husband (the two are now divorced) her best friend, but her sexual attraction to him had faded long ago. Instead she funneled all her romantic feelings toward God.

Briggs is also refreshingly open about the ways in which her faith was somewhat childlike and oversimplified: "I worried that God was mocked in some way every time I did not obey Him. And the opposite was true as well. Every time I obeyed God, the angels would fall at His feet in adoration. ('Oh, God, you are truly great. Even Carolyn obeys you!') I imagined the cosmos swirling about me, all eyes on the little gladiator of faith."

But the constraints of Briggs' faith and her church weren't lost on her, even when she was most firmly in the grasp of Fountain of Joy. When she became pregnant with her second child, her nausea was so bad that she couldn't hold down her food, and her weight dropped dangerously. Still, the fellowship frowned on "unnecessary" medications of any type, which meant she didn't feel free to take the anti-nausea drugs that had helped her through her first pregnancy safely. Instead, the congregation prayed over her and urged her to trust in the Lord. He did come through (the baby was born healthy), but when Briggs later became pregnant for the third time, she took the pills on the sly.

Briggs is also unsparing about the small-mindedness of the group of men who ran the church, despite the fact that she genuinely liked and trusted them. When her husband's company was getting ready to move operations to Arkansas, it offered him a spectacular job opportunity there. But if he chose to stay in Iowa, he would be left with no job at all. Still, the elders discouraged the couple from moving away from Fountain of Joy, claiming it would result in certain "disaster." The elders drew up a list of criteria that the couple's new church had to meet -- criteria that were so exacting that Briggs and her husband could not find a church to meet them. As a result, Eric turned down the job and kept his family in Iowa; their financial struggles were so harsh that, when Eric's company offered him another opportunity in Arkansas three years later, the couple jumped at it, Fountain or no Fountain.

And the community of loving, caring women had a tyrannical side as well. Briggs describes an episode in which, while babysitting for a friend's child, she realized that she was fully expected to nurse the infant. She recoiled despite herself: "He felt different from my babies; his body was hard and angular, his luminous gray eyes feral and accusing. He didn't smell like my young. He was of Paulina, yeasty like her, foreign and grown in humus not my own. I knew instantly there was no way I could nurse a baby that was not mine." Instead, Briggs rocked and sang to the screaming baby, feeling guilt and shame and ultimately bursting into tears herself over her inadequacy. "My body was my own. I was not submitting to God for His use, not with my whole heart, not with my whole mind, and certainly not with my body."

Briggs loses some of her focus when she begins describing the changes that led her away from her faith: Most significantly, she decided to get a college degree, which opened up her world both intellectually and sexually.

But then, you get the sense that she's describing her slow, gradual reverse transformation -- from a bridelike soldier of Christ to a freethinking, questioning woman -- as clearly as anyone could. Briggs harbors few illusions about her old self. She's fully aware of what a pain in the ass she was in the days when she was beaming with love all the time, handing out Bibles and quoting Scripture to anyone who'd sit still long enough.

But the thing that makes "This Dark World" so affecting, aside from Briggs' clear, resonant prose, is that she makes us understand that leaving her faith behind was the single hardest thing she's ever had to do. Her religious friends bemoaned the fact that she had turned away from the Lord. But no matter how her spiritual beliefs have changed, has He really lost her? The person she became because of Him is still vital and thriving, and probably more alive than ever.