In recent months, Cardinal Walter Kasper has received a tremendous amount of attention, with commentators from several arenas referring to him as “the pope's theologian.” In certain ways, the catalyst for the enhanced interest in this longtime theologian and former president of the Secretariat for Christian Unity is his recent volume, Mercy: The Essence of the Gospel and the Key to Christian Life. In Pope Francis’ first Angelus address, the pope singled out this text, noting, “This book has done me such good.” As William Madges remarks in the “Translator's Preface,” it is not hard to see that “the central themes of this book prefigure key elements in Pope Francis’ vision of the church's mission and his own pontificate” (ix). Like Francis, Kasper seeks to engage rich and complex theological questions in ways that speak meaningfully to the experience of contemporary men and women.

Readers will soon see why this volume is worthy of all the attention that it has received. Kasper's treatment of mercy is actually a tour-de-force examination of the doctrine of God from scriptural, philosophical, historical, systematic, and contemporary perspectives. Kasper laments that the Christian tradition has long focused on metaphysical attributes of God (God as Being Itself, all-knowing, all-powerful, etc.) while ignoring God's mercy as a less definitive attribute, revealed primarily in history. A failure to fully account for divine mercy is not only contrary to the biblical witness; Kasper argues that it constitutes a “pastoral catastrophe” (11). Drawing on biblical roots, Kasper shows that images of God's mercy abound in both the Old and the New Testaments as the primary way in which humans experience the divine and thus come to know themselves, their freedom, the limits of evil, and the nature of salvation. Kasper queries his readers: if mercy is at the center of the scriptural witness, why is it at the margins of doctrinal theology?

Kasper makes the argument that God's mercy is the truest expression of the divine essence. In mercy, God reveals God's true self. Moreover, divine mercy is not a threat to the classical attributes of God, such as immutability; rather, it is precisely God's mercy that demonstrates divine transcendence, omnipotence, and justice. Kasper argues that divine mercy and justice are necessarily compatible. In mercy we see that God is not subject to some external or arbitrary justice; indeed, mercy is a sign of God's absolute freedom because it is the “expression of the gracious internal obligation that God has to himself” (55). In the latter chapters Kasper considers whether secular societies are obliged to be merciful or whether mercy is a particularly Christian value. He notes that for many contemporary men and women it is senseless to renounce violence or the idea of “an eye for an eye” because vengeance seems needed to stem the spiraling atrocities of the twentieth and twenty-first centuries. Yet, Kasper argues, in light of these horrific experiences “it has become clear that, however much mercy, forgiveness, and pardon are superhuman acts, they are nonetheless highly sensible acts” (141).

Kasper's book is extremely impressive in its scope, depth, and ability to engage a wide variety of readers: academics, college students, and interested lay readers. It calls for Christians to reconsider their understanding of God and argues in a compelling way that mercy must be at the heart of this renewed understanding—and at the heart of their own lives and the life of the church. Also noteworthy is that the English translation is excellent, with helpful notes from the translator. Some of Kasper's work in the past has not been well translated, a reality that may have hindered an even more enthusiastic reception of his work in the United States. One small lacuna in this text is the lack of a concluding chapter that would help readers to synthesize and reflect on the substantive insights that Kasper presents. Even among Kasper's already considerable achievements in Catholic theology, Mercy stands out as a timely and important contribution. Readers will come away agreeing with Pope Francis that this book has done them “such good.”