This fall, in churches throughout America, worshippers are hitting the books to search for answers to the question: “What on Earth am I here for?”  But it's not the book you might think of.

Last month, over 4,000 churches began a 40-day campaign to explore the ideas about faith and the meaning of life presented in Rick Warren's bestseller, “The Purpose-Driven Life: What on Earth Am I Here for?"

Advocates say the program, used at Christian churches across many denominations, is revitalizing faith at parishes. But critics are skeptical of the self-help approach to spirituality.

The book is a how-to guide for living a Christian life. Warren, the pastor of Saddleback Church (search) in Lake Forest, Calif., lays out five main God-centered "purposes" meant to give meaning to people's lives — worship, fellowship, discipleship, ministry and evangelism.

“To discover your purpose in life, you must turn to God’s word, not the world’s wisdom,” he writes as he goes on to link each of the five purposes to Biblical Scriptures.

The book is reaching people seeking a higher purpose, while also offering Christians a new understanding and relevance for their faith, according to Rick Stillwell, pastor of Fairview Baptist Church (search) near Shawnee, Okla., whose parish is participating in the Purpose-Driven campaign.

“One of the greatest challenges we face is showing the relevance of God to our lives today,” said Stillwell. “'The Purpose-Driven Life (search)' is not a fad. Although it’s very professional and organized, it’s still transforming lives."

However, Kenda Creasy Dean, an assistant professor at Princeton Theological Seminary, views the campaign mostly as savvy marketing by the book’s publisher, Zondervan.

“This book is designed to help church leaders lead the life they preach about, but the danger is that there is no one-size-fits-all method of spiritual formation,” she said.

There's no doubt that "The Purpose-Driven Life” has touched a nerve. The book has sold over 8 million copies since it came out in October 2002. When it was released, the publisher launched the first “40 Days of Purpose” campaign in which 1,500 churches participated. This year, the campaign was re-launched and more than twice as many churches signed up.

Churches officially participating in the campaign paid a registration fee from $750 to $1,150, depending on the size of the church, which included a resource kit of sermon outlines, videos, group curricula and promotional materials.

As part of the campaign, churches have organized weekly sermons and formed small groups to discuss the book's topics. Every day, church members read one of the book’s brief chapters on their own, and each week, one of the five main purposes is introduced at the Sunday service.

Teri Sowinski of Union City, Ind., leads a small group at her home and said she enjoys bringing people together who are at different stages of their faith.

“It’s rejuvenating to bring those who might feel burned out with their faith together with many who haven’t been to church in years,” she said.

“We’re learning how to put our faith into practice beyond Sunday mornings,” said Sowinski, who is working on a Christmas mission project because of the book.

As the campaign nears its end, she is also seeing an energized spirit at church. At the coffee fellowship between Sunday services the room is so crowded, it’s hard to get inside, she said.

Stillwell’s parish is also experiencing growth as a result of the Purpose-Driven campaign.

“We’re seeing people of those hard-to-reach ages coming and taking a new approach to things they might have been turned off by before,” said Stillwell.

Dean said “The Purpose-Driven Life” has essentially given churches strategy for reaching parishioners who have become disenchanted. In the last half of the 20th century, she said, churches have become more like corporations, and in the process "have lost their soul."

"The truth is that many churches are so rudderless that any intentional plan or sense of direction is an improvement, which is partly why Rick Warren's "Purpose-Driven" language is so appealing," she said.

And despite its appeal, Dean said the book's message is not new.

“It’s really just back to the basic biblical principles,” she said.

Whatever the reason for its popularity, Stillwell contends that the campaign and the book are having a positive effect merely by bringing parishes together again.

“People for the first time in decades are recognizing church as a community of people.”