Book excerpt: In a growing secular society, what distinguishes a Christian from a non-Christian? Is a Christian identified by certain religious and ceremonial activity, social action, principles, or do their relationships identify them as Christian? This book suggests that a Christian person is in a continual relationship with the Triune God through the Holy Spirit. Furthermore, this living relationship reflects the eternal relationship of the Father, Son, and Holy Spirit, because people have been created in the image and likeness of the Triune God. This book uses historical, theological, philosophical, and biblical approaches to understand the Christian person. Throughout this book, the reader will be engaged with the modern Greek theologian, John Zizioulas. However, this book is a study on the person of the Holy Spirit, though never separated from the trinitarian relationship, who makes a human person a Christian.