Faithful members of Oprah Winfrey's TV flock know what's happening when guests start talking and their leader keeps saying "Amen," "Preach it" or even, "Sister, I understand the whole God connection!"

The host wants the guest to start "testifying," a confessional process in which believers look for God's healing hand in life's hard lessons. Winfrey learned all about "testifying" as a girl back in the Faith United Mississippi Baptist Church, where jealous peers often called her "Miss Jesus."

But here's the irony, noted journalist Marcia Nelson, author of "The Gospel According to Oprah." Winfrey has become a billionaire and one of world's most powerful women by baring her soul and urging millions of others to follow her example, resulting in what some critics call the "Oprahfication" of America. However, it's almost impossible to answer this simple question: What does Oprah believe?

"She sounds like a person who was raised in a Baptist church," said Nelson, who spent months digging into Winfrey's beliefs on suffering, gratitude, generosity, forgiveness and other spiritual topics.

"Still, it's hard to put a label on Oprah because she refuses to let people do that to her. ... You'd have to say that she looks a lot more like a Protestant than she does a Catholic, but what does that mean? It's hard to say what a person needs to believe these days to be called a 'Protestant.' "

Winfrey retains the ability to slip smoothly into the "mother tongue" she learned as a child in black churches, noted Nelson. For a few years as an adult, she attended the Trinity United Church of Christ, a progressive congregation in Chicago known as Sen. Barack Obama's home church. Then, during her "Remember Your Spirit" period in the 1990s, conservatives criticized her ties to Marianne Williamson ("A Return to Love") and other "New Age" writers who blurred the lines between Christianity and other faiths.

The key is that Winfrey has been a trailblazer who symbolizes many contemporary religious trends.

* Many Americans, said Nelson, are drawn to a "practical, how-to, self-help, just-do-it" approach to faith and personal growth that meshes smoothly with the parade of counselors, doctors, writers and ministers -- of every conceivable faith -- featured on "The Oprah Winfrey Show." It's crucial that the host looks straight into the camera and says: "This works."

Thus, noted Nelson, Winfrey has "been roundly criticized for making the spiritual too psychological, too therapeutic, too soft, too easy, too self-centered. The gospel according to Oprah doesn't appear to require some kind of doctrinal commitment or a community to ensure that the life-changing 'Aha!' moment of decision is more than a new year's resolution that is quickly made in isolation and broken two weeks later."

* The public loves complex, conflicted celebrities and Winfrey is the spiritual superstar. She quietly supports humble projects near home, yet courts publicity by flying off to start gigantic projects around the world -- such as the new $40-million Oprah Winfrey Leadership Academy near Johannesburg.

She tells women to love themselves the way they are, but keeps offering weight-loss tips. She urges viewers to give to others, but also pamper themselves. Winfrey says women should embrace their maturity, but shows them how to look 10 years younger. She advises women on private moral dilemmas, but fiercely guards her own privacy.

* One of the fastest growing segments of the population consists of people who call themselves "spiritual," but not "religious," noted Nelson. Winfrey clicks with media-driven, postmodern believers who stress the importance of personal experience and storytelling over the authority of religious institutions and doctrines. Meanwhile, many churches are trying to shed old names and labels, calling themselves "community churches" and adopting other post-denominational names.

The bottom line, said Nelson, is that for generations Americans were able to rally around a kind of tame, "nominal" Judeo-Christian faith that let them affirm a few common traditions and many old-fashioned values. But this has become harder after waves of immigration from the Middle East, Asia, Africa and elsewhere.

American is becoming more pluralistic on faith issues and that has always been just fine with Winfrey. She is all about spirituality, not doctrine. If she has a creed she keeps it hidden.

"Oprah's clothes may bear labels, but her faith does not," noted Nelson. "I don't know what her personal beliefs are."