NEW YORK -- After she left the convent, Karen Armstrong called herself an atheist. "I used to hate religion," she says. "I loathed it in my angry days."

Seventeen books later, she is recognized as one of the great religious historians, and she has reconsidered her label.

She regards herself to be deeply religious but with no denomination. "Sometimes I call myself a freelance," she says in her melodious English accent. "I can't see any one of the great religions as superior to others. . . . I'm seeking to make sense of life, looking for its meaning and how we can have a better humanity."

Borrowing for the moment from Buddhism, she explains, "Nirvana is something within you. It is not an external reality. No god thunders down from the mountaintop. Just as the great mystics in the Christian, Jewish and Muslim faiths all discovered, God is within the self. God is virtually inseparable from ourselves."

"Religion," she says, "is very complicated. Some do it very well. Some do it badly. It's an art form. Not everyone who plays the piano plays like Vladimir Ashkenazy."

Karen Armstrong is sitting in a restaurant in Manhattan sipping white wine and musing over her beliefs, her life, her work. Her new book, "The Great Transformation: The Beginning of Our Religious Traditions," is the second in a two-book deal, the first being "The Spiral Staircase," her enthralling account of her Catholic upbringing and her falling away from the church after leaving the convent in England. Knopf, her publisher, is so confident of its success that it has printed 100,000 copies.