“The mystery of the Most Holy Trinity is the central mystery of the Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them.” (Catechism of the Catholic Church 234). Over the last hundred years, Christian theologians of all confessions have insisted upon this point and undertaken what some call a renewal or retrieval of Trinitarian theology. At the same time, as St. Augustine warns at the beginning of his great work on the Trinity, “There is no subject where a mistake is more dangerous, or the search more laborious, or discovery more advantageous than the unity of the Trinity: of the Father, the Son and the Holy Spirit.” If we take St. Augustine’s warning seriously, perhaps it we should listen first, not to modern theologians, but to the Fathers and Doctors of the Church. This has been the tack of one of the main Catholic contributors to recent Trinitarian theology: the Dominican Fr. Gilles Emery. In this interview, he discusses his acclaimed studies on the Trinitarian theology of St. Thomas Aquinas.

Fr. Gilles Emery, a member of the Order of Preachers, is professor emeritus of the University of Fribourg, Switzerland, where he taught dogmatic theology from 1995 to 2021. A member of the International Theological Commission from 2004-2014, he is chief editor of the journal "Nova et Vetera," and a member of the Pontifical Academy of Saint Thomas Aquinas. He has published several acclaimed books, in French and English, on the theology of Thomas Aquinas, Trinitarian theology, and the theology of creation.

  1. The Trinity: An Introduction to Catholic Doctrine on the Triune God
    by Gilles Emery OP
  2. The Trinitarian Theology of St. Thomas Aquinas
    by Gilles Emery OP
  3. The Oxford Handbook of the Trinity
    edited by Gilles Emery OP and Matthew Levering
  4. Trinity, Church, and the Human Person: Thomistic Essays
    by Gilles Emery OP
  5. Trinity in Aquinas
    by Gilles Emery OP

From your PhD dissertation on, your research has focussed on the Trinitarian theology of St. Thomas? What prompted you to focus on the Trinity, and why have you chosen St. Thomas as your guide?
Since my early years, when I was 17 or 18, I have always been interested, if not fascinated, by the two central mysteries of the Christian faith: the Trinity and the Incarnation. So, when I began studying theology, I had a special interest in dogmatic theology.

My first love was not for St. Thomas, I must confess. I was more interested in Barth and in twentieth-century German theology in general. Little by little, under the influence of Fr Jean-Pierre Torrell, I moved over to Aquinas. I discovered that, in Aquinas, I could find answers to the questions raised by modern theologians. Moreover, I found that his answers were better than the theories elaborated during the past century or that, in dialogue with contemporary and modern theologians, Aquinas offered a great path for a deeper understanding of theology in general and the central mysteries of the Christian faith: the Trinity and the Incarnation.

After I was ordained a priest and did some ministry in Geneva, Switzerland, I came back to Fribourg for a PhD. I decided to study the relationship between the Trinity and creation in Aquinas. This was the natural continuation of what I had done before. To tell the truth, I have been working at my PhD since then. It was completed by 1994 but it will never end. For me, it is still unfinished and I still find new things every time that I study Aquinas.

The Trinity is the source, centre, and end of our life. The Trinity as the God that created us, loves us, and brings us to beatitude, is worthy of meditation, prayer, and study. As long as my superiors give me some time to do that, I would like to go on studying it.

Aquinas’s theology is still in living contact with the theology or doctrine of the Church Fathers. In a sense, he is still one of them.

Over the last hundred years, major theologians of all confessions have championed a retrieval and renewal of Trinitarian theology. In the Catholic tradition, Karl Rahner and Hans Urs von Balthasar are often considered the main contributors to contemporary Trinitarian theology. Why did you find St Thomas more convincing than them?
You mentioned Rahner and Balthasar. I would add Karl Barth. He had much influence in rediscovering the Trinity. On the one hand, Karl Rahner wrote his works, knowing what Barth had done before him. On the other hand, Balthasar developed Barth’s thought. Both are indebted to him.

What did I find in Aquinas? First, Aquinas’s thought about the mystery of the Trinity is in direct continuation with the Church Fathers. This is not so visible in my publications, but in in the courses I give at the theological faculty in Fribourg, I always begin with a semester-long exploration of the Trinity in the Bible and the Church Fathers. Aquinas’s theology is still in living contact with the theology or doctrine of the Church Fathers. In a sense, he is still one of them. He thinks with them. He relies on them: not just Augustine, but many others too. He has the huge advantage of being consistent with the patristic reading of the Bible. The retrieval of the patristic reading of the Bible could find in Aquinas a helpful bridge. He retrieved it. With his help, we can too.

Second, Aquinas is especially good at making connections between the mysteries of the faith: between the Trinity, Christ, the sending of the Holy Spirit, the apostolic Church, preaching, sacraments, moral life, and so on. He helps us see the coherence and consistency of theology, always in the light of the Trinity, and without contradiction. His contribution in this regard is unique. If it is not unique, it is of the highest value, at least. I did not really find this in contemporary writings. As every theologian knows, Rahner reproached the Augustinian and Thomistic traditions for having brought the Trinity into splendid isolation. This may be true of some of the textbooks written in the late nineteenth or early twentieth century. It is not true of Aquinas.

Third, there is the rational consistency of Aquinas’s thought. The requirements for doing theology are very high for him. He never sets out to prove the Trinity. He is very clear and explicit about that. On the one hand, he wants to show how the Trinity illuminates the entire Christian faith and life. On the other hand, he wants to show that faith in the Trinity is not contrary to reason but both plausible to natural reason yet above natural reason. The mystery of the Trinity is coherent, consistent, and plausible within the light of human reason. On this basis, we can appreciate how the Christian faith is intelligible. It is not superstition, but has rational grounds. If there are objections to faith in the Trinity, we, as theologians or Christians, can show that these objections are either wrong or do not have the force of necessary arguments. This makes us free to believe, not just with our affectivity and our emotions, but with our entire person: emotions, affectivity, and reason too. This is particularly important these days. There is a strong tendency toward fideism, especially among young students. We have to form a new generation, not to become rationalists, but to attain a detailed and fully developed understanding of Christian doctrine. Such an understanding has foundations and grounds in rational thinking, even if it depends entirely on Revelation.

When we make the sign of the cross, we begin by referring to the one divine essence and then invoke each of the three divine persons in the order in which they stand to one another. First we say, “In the name of...," and then, "....the Father, the Son and the Holy Spirit.” Similarly, St. Augustine and St Thomas, the two main influences on. Catholic theology begin by examining the mystery of the divine essence, and then the Trinity of persons. However, within modern theology it is common to charge them with essentialism. According to this charge, discourse on the Trinity should not begin, as they do, with the divine essence, but with the three divine persons. Some critics, as you mentioned, even blame the purported essentialism of Augustine and Thomas for making the doctrine of the Trinity irrelevant in practice. You have addressed criticisms such as these in your writings. Briefly, could you explain why the order in which St Thomas explains the Trinity is appropriate?
Your question has a long history. It began at least with Théodore de Regnon SJ in the late nineteenth century. Then, it was taken up by Orthodox theologians and ended up in Protestant and Catholic theology.

It is not fair to Augustine. If one looks closely at Augustine’s De Trinitate, his intention is not to show that the one God is three persons, but that the three persons are one God. So, he does not begin with the essence. In my reading of Augustine, this is simply wrong and reads him through the lens of modern accounts of the Trinitity. Both Augustine and Aquinas have been read through the lens of modern German philosophy: the philosophy of absolute spirit or absolute mind, which is very monistic. Using the powerful lens of German thought led to a big misunderstanding and has influenced us all.

In Aquinas, there is not one way to set out the mystery of the Trinity, but several. Each time he writes on the Trinity, he adopts a different plan, outline, or structure. Let us stick to the Summa theologiae. In the eyes of his critics, that is where the problem lies.

For Aquinas, the divine persons are at the centre. When he speaks of God, he speaks of the three divine persons. The persons are the essence because God is one. So, to grasp the Father, the Son, and the Holy Spirit as divine persons, we need to grasp them as divine, which includes the essence. In the Summa theologiae, the essence is treated first and then integrated into our understanding of the person. This way of thought goes back to the Cappadocian Fathers. First, as St. Basil of Caesarea clearly explained, there are two aspects in our understanding of the Trinity: not in the Trinity itself, which is simple, but in our grasp or access to the Trinity, which is not. To exclude or refute the heresy of Eunomius of Czyicus, Basil had to distinguish between what is common to the three persons and what is proper to each person. Being the Father, Son, and Holy Spirit is proper to each of them. Being God, being infinite, is common to the three: it is the essence. So, we think of each divine person by what St Basil called the combination of these two aspects: the common and the proper. Aquinas builds on that by explaining that, in our understanding, what is common comes first. To understand that the Father or the Son is a divine person, first we have to grasp them as divine. It is the divine essence, common to all three persons, that accounts for the divinity of each. The method of Aquinas makes sense because he first expounds what is common to all three divine persons—the divine essence—and then he specifies what is proper to each. This may not be the way we come to knowledge of the divine persons through the liturgy or our own experience. However, it is the way that the theological exposition has to follow, to be consistent with the patristic sources: an exposition in which each steps prepares the step that follows. So, for me, the charge of essentialism in Aquinas is pointless.

I would also add that this allows the theologian to make a differentiated use of philosophy within theology. In the study of the divine essence, theology can make use of metaphysics with necessary arguments. God is one; God is good; God is wise. Of course, for this we have the Bible. However, the teaching of the Bible can be supported by rational arguments that have force of necessity for a human mind that is thinking aright. In the case of the distinction of the persons and what is proper to each of them, there are no such necessary arguments. The method of using philosophical arguments is different. Aquinas accounts for both in the Summa. He accounts for how the three persons are divine and are at the centre. He accounts for the proper, differentiated use of philosophy within the study of the mystery of the Trinity.

Our first access to the Trinity is through the liturgy.


Several of your books have been translated into English. Perhaps the most accessible one for non-specialists is The Trinity: An Introduction to the Catholic Doctrine on the Triune God. What do you take to be most distinctive of your introduction on the Trinity. What sets it apart from other textbooks on the subject?
Well, I begin with a chapter on liturgy and the Bible. I begin with the liturgy because it comes first for most Christians, if not all. Our first access to the Trinity is through the liturgy. I would give priority to it in the order of discovery, and not just there. The liturgy is the beginning and the end of our Christian lives. It is the natural place to discover, celebrate, and live with the Trinity. So, I begin with liturgy, especially through the doxologies.

Then, I move on to the Bible: the Old and New Testament. If I had to rewrite this book, I would develop the section on the New Testament. There is much more to say, but this book had to be short. It is a textbook. The genre requires short chapters.

Then, I look at the Church Fathers, the development of the doctrine of the Trinity during the first centuries, up until Constantinople I and Gregory of Nyssa in the east and Augustine in the west. Then there is a speculative part. It deals with St Thomas and contemporary questions.

This is close to what I taught in my courses for students during the first years of the first cycle theology degree.

Is this book very different from other introductions? This book sold much better than other books of mine because the audience is broader. It is not just meant for specialists, but for a much larger audience, and it has been translated into several languages.

The difference is that I give more weight to the foundations of Trinitarian theology, namely liturgy and the Church Fathers. I do not begin with contemporary problems: the question of the immanent and economic Trinity, or whether the mystery of the Trinity is revealed only in the Cross of Jesus Christ, and so on. No, I begin with the basic foundations: liturgy, Bible, Church Fathers. Perhaps, I should have developed a section on contemporary discussions of Trinitarian theology at the end. However, this book is meant to be short and to give an introduction. So, I had to make choices and limit myself to what I thought was a priority: liturgy, Bible, and tradition. Nevertheless, I wrote the chapters on liturgy, Bible, tradition, and Aquinas with contemporary questions in the background. Every line I wrote tried to answer contemporary questions, even when I did not mention them explicitly.

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