With his papal election, Ratzinger became the first Pope to become a theologian in the true sense of the word. And, as a "cooperator of the truth", he consolidated the lines along which he was working, the lines needed by the Church at the beginning of the third millennium. Before addressing the fourth theological stage of Benedict XVI's life as Pope, it is worth making two points. 

The profile of an important theologian is shaped, first of all, by the clichés that everyone repeats and which are embedded in the histories of theology and dictionaries. They are often well founded. In Joseph Ratzinger, one speaks of expanded reason, the dictatorship of relativism, relational anthropology, personalism and the Augustinian primacy of love, attention to the liturgy, ecumenism... Then, his profile is marked by his best known books Introduction to Christianity, report on faith, Jesus of Nazareth, and his lectures as prefect... These are the sources for studying him.

But the edition of his complete works (O.C.), as we have already noted, has transformed this.

 Because, for example, the two thesis , on St. Augustine and on St. Bonaventure, which are the most extensive and systematic programs of study of his academic period, have emerged. And two volumes have been composed with all his commentaries on the Council, which are a very relevant work of his time as a professor. And there is another entire volume dedicated to the priesthood. In addition, the small guide on Eschatology, with the addition of other materials, has also become a powerful volume. So the sources for studying Ratzinger are not the same now as before. 

Another nuance. By becoming Pope, he is no longer a private theologian, but constantly exercises a public Magisterium. This affects his theological profile in two ways. Not everything he writes becomes Magisterium. And also not everything he teaches as pope is exactly his theological opinion. 

As John Paul II did in Crossing the Threshold of Hope or in his memoirs, there are writings of Joseph Ratzinger that only express his opinion staff, and are not Magisterium. In Jesus of Nazareth he expressly states this. But the same is true of the conversations with Seewald(The Light of the World, 2010) and other moments of expansion. 

It is also the case that not all of his Magisterium expresses exactly his way of thinking, because much of what he preaches was not written by him. It was written by those who help him with their approval and, depending on the case, with their guidance or corrections. And it is ordinary Magisterium because it represents what the Church believes. That is not a problem. But it does not necessarily reflect its theological approach or its style staff. It is necessary to take this into account when making syntheses of his thought or doctoral thesis . It is not useful to cut and mix all subject of materials. 

For example, the beautiful cycles he developed in the audiences on the origins of Christianity, St. Paul, the great ancient and medieval theologians, the Doctors of the Church, and prayer, are pleasing and useful for teaching. And they are there because he wanted them to be. But it would not make sense to draw his theological thought from them. He did not write them down. 

Obviously, a perfect discrimination between what he wrote and what he did not write is impossible. But it is possible to think about what theological inspirations his Magisterium had and what he actually did with them. 

In order to know what he wanted to do as pope, there are three very personal and relevant first texts, which we will recall in a moment. 

Then we must review what he did and what he promoted. First of all, the encyclicals and apostolic exhortations, which, even if he did not write them in their entirety, represent his main lines. 

Ecumenical endeavours stand out, goal an important feature of the entire pontificate, and deserves a separate study. 

There are interventions where he is very personally involved, such as the trips to Germany (the German Parliament). Perhaps the failed lecture at La Sapienza (2008) or the intervention at the UN (2008), or his speech in Westminster to the British Parliament (2010)... There are also moments where his voice is very staff: meetings with priests or seminarians or compatriots, interviews with Seewald.

And, of course, the most theological staff and a longing of his life is the book Jesus of Nazareth, written with heroic tenacity and perseverance. 

On 18 April 2005, Cardinal Ratzinger, as Dean of the sacred high school, presided at the Mass before the conclave in which he was to be elected pope. He gave a famous homily. He spoke of the threat of a "dictatorship of relativism" and of the Christian response: "A faith that does not follow the waves of fashion and the latest novelty: adult and mature is a faith deeply rooted in friendship with Christ. [...] We must lead the flock of Christ towards this faith. Only this faith creates unity and is realised in charity". He relied, as always, on a Christian truth spoken in charity. 

On 20-IV-2005, after being elected and celebrating Mass, he addressed the cardinals. After recalling John Paul II, he called for ecclesial communion, topic of the Council. And he said "I wish to reaffirm with force my firm determination to continue in the commitment to implement the Second Vatican Council, following the example of my predecessors and in faithful continuity with the two thousand year tradition of the Church". And since it was the year of the Synod on the Eucharist, he added: "How could I fail to see in this providential coincidence an element which must characterise the ministry to which I have been called?He pledged to "do everything possible for promote the priority cause of ecumenism", to "continue the promising dialogue begun by my venerable predecessors with the different cultures" and to "propose to the world the voice of the One who said: 'I am the light of the world'",especially to young people. 

But the most surprising text is his Christmas greeting to the Roman Curia that year (22 December 2005). He took the opportunity to see where the Church stood. To judge the application of the Council, which was a reform and not a rupture, and in many points remains to be applied. He reviewed the great questions of evangelisation in relation to the modern world, with three questions: dialogue with the sciences (including exegesis), dialogue with political thought and inter-religious dialogue. And, in passing, he gave a theological answer on religious freedom, which was one of the reasons for Lefebvre's schism. A text to reread, underline and summarise. Really, a core topic of the intentions and approach of the pontificate. 

Of Benedict XVI's three encyclicals, the first, Deus caritas est (2006), is perhaps the most important staff. According to Seewald's biography, the second part was already more or less ready: charity in the Church, in relation to welfare and charitable work, with the intention of insisting that the Church is not simply an NGO, and that it lives from the charity of Christ. A magnificent first part was added on what is love and Christian love. Reading it, one finds, especially at the beginning, Ratzinger's style. Spe Salvi (2007) also takes up a concern staff of Benedict XVI: hope, as a Christian look into the future, into God's salvation. With its obscuring and modern attempts at political and economic substitution. And the places where it can be recovered: prayer, Christian action and suffering, and the longing for a definitive judgement. Some glimpses recall his guide of eschatology. 

Caritas in veritate (2009) is written in the perspective of Paul VI's Populorum progressio (1967) and came out in the midst of a global economic crisis (2008). It sought to take up the tradition of the great social encyclicals and put forward suggestions for addressing the problems of poverty in so many nations. The deflation of the communist world had made false answers and horizons disappear, but positive action was needed. Rethink the conditions of a real development . That is effective charity, and, for Christians, inspired by Christ and with his financial aid. 

There remained the outline of the encyclical on faith, after charity and hope (Lumen fidei), with its central topic We have believed in love, so typical of Ratzinger, which was caught by the change of pontificate (2013) and was left on the back burner.

The two apostolic exhortations correspond to two synods. The first one convened by John Paul II, but presided over by Benedict XVI (2005), gave rise to Sacramentum charitatis (2007). As we have seen, it seemed providential for him to focus on the Eucharist in order to revive the life of the Church. The topic of the second synod (2008) represents a certain change from the preferably pastoral tradition: the Christian reading of the Bible, which gave rise to Verbum Domini ( 2010). It reflects his concern to spread a believing approach to the Bible. That is why he is taking time out to write Jesus of Nazareth.

Of this immense material, the two trips to Germany (2006 and 2011) stand out as the most personal. And they are not to be missed. It is clear that the homily in Regensburg Cathedral and the speech at the University, his university (2006), were his own, also because of the stir caused by an anecdotal quotation on Muslim violence. In the end, the uproar was happily put right. But the main topic was very much his own: the relationship between science and faith and the public role of faith. 

On the second trip to Germany (2011), in addition to the informal meeting with journalists and the moving meeting with seminarians in Freiburg, there is his memorable speech in the German Parliament recalling the moral foundations of the democratic state and the bitter experience of how an unscrupulous group (the Nazis) could seize power. 

Of course there are many more things in so many memorable trips: the enthusiasm of Poland (2006), the entrance at the Blue Mosque in Istanbul and the meetings with the Patriarch of Constantinople (2006), the speech to the French intelligentsia (2008), the tour of Mexico and Cuba (2012). And the good times at the World Youth conference in Cologne (2005), Sydney (2008) and Madrid (2011). And, always on his travels, the ecumenical work . 

Joseph Ratzinger was always an attentive student of exegetical developments and did much to keep himself well informed, especially of the German bibliography , as is clear from the prefaces to these three books. He soon realised that, in addition to remarkable contributions, the pure historical-critical method led to locking the texts of the Bible in the past, to making them ever more distant and to concluding so many scattered hypotheses that, in reality, nothing could be concluded at all. 

But this, when applied to the life of Christ, meant leaving him locked up in the past and distinguishing almost radically the Christ of the confessed faith from the Christ of history, in reality lost. So all the claims of the Church, in perfect connection with the claims of the texts, were left up in the air. The most absurd hypotheses about how statements about the figure of Jesus Christ, his divinity, his miracles, so implausible from a purely human historical point of view, could have been composed in such a short time. Unbelievable unless they were really the work of God. If one does not start from faith, one is forced to make reconstructions that are really difficult and perfectly in the air. 

With all his knowledge, the three parts of this work are an attempt at a believing and informed exegesis, centred on faith in Jesus Christ. He was convinced of the urgency of this approach. He firmly believed that it was a service he should render. He had attempted and begun it as prefect, and had the incredible merit of carrying it out as pope. 

Obviously, his Withdrawal (2013) also raised a theological question: did he have the right to resign? There was only one precedent and in special circumstances: the Withdrawal- Celestine V's flight (1294), because others were forced to do so (Western Schism). John Paul II considered it and thought it was not possible. Benedict XVI considered it and decided that he should do it and created a reasonable precedent. 

At the end of his last book-interview with Seewald (Benedict XVI. Últimas conversaciones, Mensajero, Bilbao 2016), when he was already retired, he commented on his episcopal motto Cooperador de la verdad: "In the 1970s, I became clearly aware of the following: If we forget the truth, what are we doing all this for? [...] With the truth, it is possible to collaborate because it is a Person. It is possible to commit oneself to it, to try to assert it. That seemed to me, in the end, to be the true definition of a theologian" (292). From then until the end.