In this insightful theological study, Kevin O'Reilly explores the concept of 'in persona Christi'—the way in which the priest acts in the person of Christ during the sacraments. Drawing deeply from the works of St. Thomas Aquinas, the book provides a rigorous yet accessible examination of what it means to live out the priestly vocation. O'Reilly considers the ontological transformation of the priest and how this influences both the life of the individual minister and the life of the Church as a whole. This work is essential reading for anyone engaged in serious theological reflection on the ministerial priesthood. Whether you are a student preparing for ordination or a priest seeking to enrich your understanding of your daily ministry, this volume offers a profound reflection on the sanctity and responsibility of the clerical life. O'Reilly’s scholarship bridges the gap between ancient Thomistic thought and the contemporary challenges faced by the Church, helping you to better understand the beauty of the sacramental life.