When Catholics make the sign of the Cross “in the name of the Father, and of the Son, and of the Holy Spirit,” they express belief in what we now call “the Trinity.” No doctrine of the Catholic faith is more foundational or more mysterious. The doctrine of the Trinity expresses the most profound concept of God as relational: that is, God as Father loves and is loved by the Son and together Father and Son generate the Spirit of Love. This triune source of all life is a dynamic love-giving, love-receiving, and love-exchanging eternal source of all that exists.

This book examines the biblical sources for belief in God as “three persons,” and traces the history of this important doctrine in scripture—in both the Old and New Testaments—and in Church teaching. References to the Catholic Catechism offer theologically precise commentary that is accessible to the general reader. Contemporary reinterpretations assist the reader to grasp what is at stake in this core truth. Questions throughout the text facilitate understanding: How can this doctrine be expressed in contemporary language? How does this doctrine affect my prayer? How is God One in Three?