What defines a theologian? It seems obvious to look at the outward effect. First, in his books. Then, in the main ideas or clichés attributed to him, fixed, with better or worse success, by a tradition first of essays and, above all, of dictionary entries and manuals. In the case of Joseph Ratzinger, not enough time has passed for this operation. Nor is his work completely fixed, since his Collected Works are being published, grouping his writings by subject and bringing together unpublished works and minor or little-known writings, thus transforming their appearance and, in the long run, their readability. 

What is fixed are the four stages of his life. After a period at training, comes his work as a theologian (1953-1977), including his participation in the Council (1962-1965); then as Archbishop of Munich (1977-1981), as Prefect of the Congregation for the Doctrine of the Faith (1982-2005) and as Pope (2005-2013). This combines two further stages dedicated to theological thought or discernment, as professor and as prefect; and two purely pastoral stages, as bishop and as pope. It is a happy combination. It would be a grave error regarding the nature of theology, and a tremendous impoverishment, to reduce his theological contribution to his "professional" dedication: articles, books, conferences...  

He has done theology in all four periods, albeit in different ways. And one can try to synthesise both what each period contributes and the basic lines that run through them all. In his conversations, he himself has stated that he sees himself with a certain continuity, although circumstances have put him in different positions. Kierkegaard used different pseudonyms to show the different perspectives with which he could look at things. Joseph Ratzinger has been given them by the course of his life. For a young theologian, a bishop in a complex era, a prefect for the doctrine of the faith who has to pay universal attention to doctrine, and a pope who has to be a good shepherd and reference letter of communion for the whole Church, with a particular mission statement in the interpretation and application of the Second Vatican Council, do not see things from the same perspective. 

Joseph Ratzinger has portrayed himself very well in that exceptional and charming autobiographical book, My Life (1927-1977), which he published in 1997 and which covers his career as a professor. It is completed with the four books of conversations with Seewald and with some of the moments of conversation and expansion during his pontificate. 

There you can see how much he has been marked by the experience of faith in his childhood, in the traditional Bavarian environment, with his simple and believing family, with the liturgy celebrated joyfully and solemnly in the parishes he knew as a child, with the stages and feasts of the liturgical calendar that marked the rhythm of the life of all those believing people. He might have lost or changed these roots, but in the course of his life he has consolidated them, and this Christian experience is the basis of his theology. 

In the presentation of his Collected Works (vol. I, devoted to the Liturgy), he explains: "The liturgy of the Church was for me, from my childhood, a central reality in life and it also became [...] the centre of my theological endeavour. As subject I chose fundamental theology, because I wanted above all to follow the question: Why do we believe? But in this question was the other question of the right answer to God and thus the question of divine worship [...], of the anchoring of the liturgy in the founding act of our faith and thus also of its place in the whole of our human existence". And a little earlier he explained: "In the word 'Orthodoxy' the second half, 'doxa', does not mean 'opinion', but 'glory'; it is not a question of having a correct 'opinion' about God, but of the correct way of glorifying him, of responding to him. This is indeed the fundamental question that the man who begins to understand himself correctly asks himself: "How should I meet God?

His pathway for fundamental theology, on the nature and problems of faith, which is also addressed to the status of the modern world, will find a liturgical response. Faith can and must be thought about in order to understand, explain and defend it, but above all it must be lived and celebrated. From this he also deduces the role of the theologian and his own role. 

Joseph Ratzinger was educated at the seminar of his diocese, in Freising, and later at the School of theology in Munich (1947-1951), still in ruins as a consequence of the war. In My Life he reflects very well the enthusiastic and renewing atmosphere of the time. The harsh experiences of Nazism had aroused in the German Church a yearning for renewal and evangelization, which received with enthusiasm the new ferments of liturgical theology (Guardini), of ecclesiology (De Lubac) and of Scripture, as well as the new philosophical inspirations, especially of phenomenology and personalism (Guardini, Max Scheler, Buber). All this gave him a certain tone of overcoming (and superiority) with respect to the old scholastic (and Roman) theology. The young Ratzinger was impressed by De Lubac's Catholicism, and by Guardini's Sense of the Liturgy. And, from then until the end of his life, he would keep himself well informed of the progress of biblical theology.

Somewhat unexpectedly, he became a professor at seminar and specialized in Fundamental Theology, where the great questions of faith in the modern world, the sciences, politics, and the difficulties of people today in believing were raised. The doctoral thesis on St. Augustine(People and House of God in St. Augustine, 1953), made him delve deeper into ecclesiology. And the thesis of habilitation on The Theology of History in St. Bonaventure (1959) dealt with a new approach of fundamental theology: revelation, before being concretized in formulas of faith (dogmas) is the manifestation of God himself in the history of salvation. This confronted him with Schmaus in the tribunal of thesis , but it was an idea that was already imposing itself and would end up being taken up by the Second Vatican Council: revelation is with "deeds and words" of God, and founds the profound unity of the two sources, Scripture and Tradition. 

There followed a very intense period as professor of Fundamental Theology (and later also of Dogmatic Theology) at seminar (1953-1959) and then at four universities: Bonn (1959-1963), Münster (1963-1966), Tübingen (1966-1969) and Regensburg (1969-1977).

Ratzinger is a young and intelligent professor and feels himself linked to a current of German theological renewal with representative figures, such as Rahner and Küng, who appreciate him. He was also appreciated by Cardinal Frings, who took him on as advisor and conciliar expert, after having heard him speak at lecture about what the Council should be like (1962-1965). He worked a lot for the Cardinal (almost blind), and the Council gave him a new experience of the life of the Church and the attention with great and veteran theologians he admired, such as De Lubac and Congar. 

Within that theological enthusiasm he began to perceive the symptoms of the post-conciliar crisis and, little by little, he distanced himself from the vedetism of some theologians, such as Küng, and also from what were understood to be the true and authentic teachers of the faith, a council of theologians constituted as a permanent source of change in the Church. This will be the reason for his adherence to the project of Von Balthasar and De Lubac's journal Communio, in contrast to Rahner's journal Concilium. Discernment is needed. It is also necessary to discern and focus biblical theology, so that it brings us closer to Christ and does not separate us from him. It is a concern that is born then and grows in his life until the end when, already as Pope, he writes Jesus of Nazareth. 

At first glance, his work as a theologian is not very extensive and is to some extent hidden, because he has quite a few dictionary articles and commentaries. As a result of his work in Fundamental Theology, his Theory of Theological Principles (1982) was later published. He also brought together his articles on ecclesiology in The New People of God ( 1969) and, later, in Church, Ecumenism and Politics. New essays on ecclesiology.  

However, the book that made him famous at the time, and which brings together all his concern to explain the Christian faith to a more or less problematised and critical modern world, is his Introduction to Christianity (1968: complex year), soon translated into many languages. It is a course for university students, but it brings together and synthesises many of his views. 

In addition, when he had already been appointed Archbishop of Munich, he completed and published a brief Eschatology (1977), which is more important than it seems in his thought, since it gives the cosmic sense of history, puts human life before the great questions and allows him to approach the problem of the soul and the person from a theological point of view renewed by personalist thought. The human being is first and foremost a word from God and someone destined for him. 

It took him completely by surprise, as he confesses in all simplicity in Mi vida. Not even when the nuncio called him did he imagine what was in store for him. But Paul VI had thought of him as a theologian-bishop with sufficient authority staff to help cement the difficult post-conciliar ecclesial status in Germany. Joseph Ratzinger endured it. The most beautiful and rewarding part of his ministry was the preaching and the attention with the simple people. The hardest thing was the resistances and manias of the ecclesial Structures , so developed (and sometimes problematised) in Germany. The first is the lived faith, in which the authenticity and efficacy of the Gospel is appreciated. But the second, which is difficult to handle, is also part of the reality of the Church in this world and cannot be ignored. 

As the second part remains more hidden, it can be said that this period is characterised by a great expansion of his attention to liturgy and preaching on Christian holiness. And this consolidates his theology as a pastor, recalling the strong tradition of the ancient church fathers, theologians and bishops. The mission statement of a bishop is, above all, to celebrate and preach, as well as to guide the life of the Church. The same activity allows him to develop his liturgical thinking, and to develop his reference letter to the holiness of the Church, reflected in the mysteries of the Lord's life and in the lives of the saints. 

It is a short period, four years, but core topic in the development of his liturgical theology. What, at first, as a priest and teacher, had been occasional preaching, gradually became a body of work on the mysteries of faith and the life of Jesus Christ that the Church celebrates throughout the year. For example, the four preachings on the Eucharist, the centre of the Church (1978), The God of Jesus Christ. Meditations on the Triune God, and The Feast of Faith (1981). His liturgical reflection, previously somewhat scattered and occasional, is now consolidated in a general vision, and will end, now as prefect, in his The Meaning of the Liturgy (2000). In it he also includes his interest in art and, especially, in sacred music. 

In addition, his preaching on creation in the face of the questions of modern science and evolution stands out in this period, resulting in an intelligent and lucid book, Creation and Sin.