In Greenville, N.C., during the second leg of the Nuns on the Bus tour, Sr. Simone Campbell met a family that had driven from Lancaster, Penn., to seek help from the sisters. A mother, a father, and a daughter who appeared to be about 8 years old were desperate to prevent the father’s deportation. Campbell, a 68-year-old nun, attorney, and social justice advocate, wrapped her arms around the frantic family and began to pray in Spanish. A crowd gathered around them, and they all prayed together.

It’s moments like those, Campbell says, when she feels the Holy Spirit at work. And it is such moments that motivated her to say yes to writing a book, A Nun On A Bus: How All of Us Can Create Hope, Change, and Community (HarperOne, Apr.).

After nearly 50 years as a member of the Sisters of Social Service, Campbell (who did find help for that worried family) has learned to see most things as “Spirit driven”—even things that at first bring sorrow. In April 2012, the Vatican’s Congregation for the Doctrine of the Faith issued a Doctrinal Assessment of the Leadership Conference of Women Religious, an association whose members represent approximately 80% of the women religious in the United States.

The assessment stated, among other things, that the LCWR was not attending sufficiently to the Church’s stance on sanctity-of-life issues and same-sex marriage. NETWORK, a social justice lobby for which Campbell serves as executive director, also was named as an organization in need of review. At that moment, Campbell and her fellow sisters saw opportunity in the midst of their pain. “We had a lot of attention, and our question became: How do we use this moment for mission?” she tells PW. “It was our big question in prayer and conversation.”

The Sisters of Social Service are based in Encino, Calif., but Campbell works from Washington D.C. and is no stranger to organizing for a cause. Reaching out for advice and partnership to such organizations as Families USA, the Center for American Progress, and a variety of community action programs, the sisters decided to campaign against the budget proposed by Congressman Paul Ryan by driving around the country in a bus labeled “Nuns on the Bus.” They had no idea what the response would be, or if anyone would even take notice. But they need not have worried--in nearly every one of the dozens of cities where they stopped, crowds gathered to support their mission.

In the first leg of their trip, during which the sisters spent 15 days on the road, they covered 9 states and three dozen cities. In September 2012 Campbell’s journey led her to the podium at the Democratic National Convention, where she stressed the importance of shared responsibility for one another and spoke out against Ryan’s budget, which called for deep cuts to social services and had been endorsed by presidential candidate Mitt Romney.

“I describe my spirituality as ‘walking willing,’” Campbell says. This openness helped her say yes when Roger Freet, executive editor at HarperOne, reached out to suggest she write a book about the Nuns on a Bus campaign. Campbell knew she could write about policy but found telling her own story to be more of a challenge. HarperOne brought in Catholic journalist (and sometime PW contributor) David Gibson (The Coming Catholic Church; The Rule of Benedict) to work with her. Says Campbell, “He really pushed me to do the biography part. We wanted it to be accessible, because it’s really important that people understand the humanness of politics.”

An online study guide for the book—which has been blurbed by Nancy Pelosi and Dick Durbin and received wide media coverage—will be available soon, providing a place where readers can post stories of how faith and politics have intersected in their own lives. “I hope people see the book as a call to action and know that we’re in this together,” Campbell says. “Politics has become too much of a spectator sport. If we’re going to have democracy we have an obligation to participate, and we have an obligation to make room at the table. We’re all called to integrate our faith and values into action.”