The Cleansing of the Heart: The Sacraments as Instrumental Causes in the Thomistic Tradition, Thomistic Ressourcement Series, Matthew Levering and Thomas Joseph White, OP, eds. (Washington, DC: The Catholic University of America Press, 2017).  *Paperback edition, March 2025.  

Abstract: 

Recalling the Biblical and Patristic roots of the Church's sacramental identity, the Second Vatican Council calls the Church the 'visible sacrament' of that unity offered through Christ (LG 9). 'Sacrament' in this sense not only describes who the Church is, but what she does. In this regard, the Council Fathers were careful to establish a strong connection between the symbolic nature of the Church's sacraments and their effect on those who received them.

This book is concerned with the cleansing of the heart—a phrase borrowed from St. Augustine and employed by Aquinas, which describes the effects that natural elements such as water or bread have on the human person when taken up by the Church as sacramental signs. Aquinas' approach to sacramental efficacy is unique for its integration of diverse theological topics such as Christology, merit, grace, creation and instrumentality. While all of these topics will be considered to some extent, the primary focus of The Cleansing of the Heart is the sacraments understood as instrumental causes of grace. 

This volume provides the historical context for understanding the development of sacramental causality as a theological topic in the scholastic period, emphasizing the unique features of Aquinas' response to this question. Following this, relevant texts from Aquinas' early and later work are examined, noting Aquinas' development and integration of the idea of sacramental causality in his later work. 

The Cleansing of the Heart concludes by contrasting alternatives to Aquinas' theory of sacramental causality that subsequently emerged. The rise of humanism introduced many changes within rhetoric and philosophy of language that had a profound effect on some theologians during the Modern period. This book provides historical context for understanding the most prominent of these theories in contrast to Aquinas, and examines some of their theological implications.  

Awarded The Journet Prize (2018)

Conferred by the Aquinas Center for Theological Renewal, the Journet prize honors the scholarly monograph published in any language during the past calendar year that best exemplifies the task of drawing upon the thought of St. Thomas Aquinas to engage constructively in contemporary theology, philosophy, and/or biblical studies. 

Reviews:

“The importance of what Lynch has accomplished in this work cannot be overemphasized. The scholarship is of the highest quality. Simply put, there is no theological work within the last fifty years that treats this topic with as much clarity as Lynch does in these pages. His engagement with Aquinas’s major commentators, teasing out their key lines of insight and development, makes this volume of value to all students and scholars of sacramental theology.”

Roger Nutt, The Thomist 84.3 (2020) 

“In this clearly written and well-informed study, Fr. Reginald Lynch, O.P., provides an excellent exploration of different theories of sacramental efficacy as divine instrumentality, especially the theory of Thomas Aquinas… The work succeeds both as an introduction to the study of sacramental efficacy, and as a solid study of Aquinas and Cano. Eminently satisfying.”  

Thomas Sundaram, First Things (August 2018) 

"This book represents an important and well-researched contribution, showing Lynch to be someone whose work is clearly to be reckoned with...Systematic theologians and historians of theology will find in this volume a stimulating case for the historical interest and ongoing theological value of the Thomistic view of sacraments as instruments of divine activity. Philosophical readers should not overlook this book either, as it provides important insights about medieval theories of causality. Discussions of how sacraments communicate grace constitute one of the main contexts in which a medieval author could develop a theory of instrumental causality, and those of us who work on medieval philosophical thought ignore these discussions to our own impoverishment."

Therese Cory, The Journal of Theological Studies 70 Iss. 2  (2019) 

“Clearly written and authoritatively referenced, even if dense and highly technical, The Cleansing of the Heart is both a first-rate history of the Thomistic theory of sacramental efficacy and a robust apologetic for it.”  

Thomas M. Kocik, Antiphon 22 n. 3 (2018) 

“Reginald Lynch offers in his work a concise and clear account of the meaning and development of Thomas Aquinas’ views of sacramental causality. The Cleansing of the Heart is primarily a work of speculative theology, but its philosophical background and systematic approach make this interesting not only to Thomistic philosophers and theologians but also to scholars who are generally interested in the sacraments, causality, grace, and the development of theology.”

Catherine Peters, European Journal for the Study of Thomas Aquinas 38 (2020) 

"Lynch shows how the Thomist understanding of the sacraments forms a sapiential synthesis of the most vital aspects of theology (anthropology, Christology, grace, merit), all of which converge on the question of sacramental instrumental causality, which stands “at the heart of the Christian mystery” (205)."  

Joshua H. Lim, Nova et Vetera (English) 15.2 (2022)