Children of God in the World is a textbook of theological anthropology structured in four parts. The first attempts to clarify the relationship between theology, philosophy and science in their respective approaches to anthropology, and establishes the fundamental principle of the text, stated in Vatican II's Gaudium et spes, n. 22, "Christ manifests man to man." The second part provides a historical overview of the doctrine of grace: in Scripture (especially the teaching of the book of Genesis on humans 'made in the image of God', as well as Paul and John), among the Fathers (in particular the oriental doctrine of 'divinization' and Augustine), during the Middle Ages (especially Thomas Aquinas) and the Reformation period (centered particularly on Luther and the Council of Trent), right up to modern times. The third part of the text, the central one, provides a systematic understanding of Christian grace in terms of the God's life present in human believers by which they become children of God, disciples, friends and brothers of Christ, temples of the Holy Spirit. This section also provides a reflection on the theological virtues (faith, hope and charity), on the relationship between grace and human freedom, on the role of the Church and Christian apostolate in the communication of grace, and on the need humans have for divine grace. After considering the relationship between the natural and the supernatural order, the fourth and last part deals with different philosophical aspects of the human condition, in the light of Christian faith: the union between body and soul, humans as free, historical, social, sexual and working beings. The last chapter concludes with a consideration of the human person, Christianity's greatest and most enduring contribution to human thought.