After Pope Emeritus Benedict XVI resigned from the papacy in 2013, he never stopped thinking or writing. Near the end of his life, he and editor Elio Guerriero gathered together a whole volume of new material, dealing with the themes closest to his heart. The pope asked that it be published upon his death.

This final work is What Is Christianity? It takes up a kaleidoscopic array of themes: the Christian faith's relationship with other religions, especially Judaism and Islam; the theology and reform of the liturgy; the priesthood; the saints; the Eucharist; the tragedy of abuse; the beauty of nature; Italian and German culture; and much more.

With prophetic insight into our times, Benedict warns of a "radical manipulation of man" in the name of tolerance, insisting that the only "authentic counterweight to every form of intolerance" is Christ himself—and Christ crucified.

A lifelong Catholic, the late pope pays tribute to some of the giant figures of Christianity who have served him through the years as guiding stars: his predecessor Pope John Paul II, the 20th-century German Jesuit martyr Alfred Delp, and the silent carpenter Joseph, his patron saint.

What Is Christianity? is a frank spiritual testament from a theological master, a churchman who loved the faith of simple Christians but who always stood ready, even in his last days, to dialogue about every aspect of human life—in love and in truth.