Ashley Smith is credited by police with playing a role in ending the 26-hour hunt for Brian Nichols, who's accused of killing a judge and three others.
Smith told reporters later that "The Purpose-Driven Life" was instrumental in keeping Nichols calm.
Nichols, 33, surrendered to a heavily armed SWAT team afterhad a soulful conversation with him about the book, which she'd been reading, reports The Early Show national correspondent Hattie Kauffman.
"I got a book. "The Purpose-Driven Life," Smith said at the time. "I turned it to the chapter I was on that day, chapter 33, and I started to read the first paragraph. After I read it, he said, 'Stop. Will you read it again?' I said, 'Yeah, I'll read it again." She wiped away a tear.
The book was a mega-hit even before the incident. Its phenomenal success, Kauffman says, mirrors that of its author, Pastor Rick Warren.
He and his wife started Saddleback Church in a rented apartment in 1980. Now, there are followers worldwide, and their headquarters in Lake Forest, Calif., is a 120-acre campus, where more than 20,000 people come to worship every week.
The church has a huge cathedral, live band, giant video screen, and a star - Warren.
"The whole reason you are alive," Warren says, "the reason your heart is beating right now -- there's only one reason for it. God made you to love you. That's why you're alive. There's no other reason you're alive. God made you to love you."
In his trademark Hawaiian shirts, Warren preaches a simple message: Life is not about you. Turn yourself over to God, and amazing things will happen.
It's a message he takes around the world, most recently, to Rwanda, whose president invited him after reading "The Purpose-Driven Life."
Another book, "The Purpose-Driven Church," caught the eye of Forbes publisher Rich Karlgaard: "I thought, you know, this is one of the greatest entreprenuerial books I ever read, and if you substitute business for church, it's just a terrific guide."
Smith says the books turned her life around. They may have saved her life as well, Kauffman observes.
Warren tells The Early Show co-anchor Harry Smith his "first response was to feel sad for family members of the people killed before Ashley got Brian to turn his life in, but I was very excited to hear that she had used the book to teach him that he had a purpose, that he had meaning in his life and that there was a reason for hope.
"You see, the reason Brian was acting the way he was is, when people feel hopeless, they act in hopeless ways. And he was clearly acting that way and she showed him that there's a reason for hope."
Warren says Smith drew the courage to get through her time with Nichols because, "When God is inside of you, it gives you courage to do the right thing. Courage isn't the absence of fear it's moving ahead in spite of fear."
Another theme of the book, and one one Warren's main principles, is, "We're meant to serve God, but the way we serve God is by serving others. …And in the same way, God takes pleasure in watching us be us. And yet that kind of unconditional love is…so rare in our world because we live in a world of conditional love. …God say, 'I love you, period.' …And Ashley was able to communicate that love to Brian, and he responded."
"The Purpose-Driven Life" has passed the 20 million copy mark, and was the best-selling book in the world in 2003 and 2004, an achievement it is expected to repeat this year as well, Warren says.
To read an excerpt of "The Purpose-Driven Life," click here.