In the encyclical letter synod Ut Unum Sint, on the commitment to ecumenism, St. John Paul II spoke of the need for the Church to "breathe with her two lungs" (par. 54). This evokes the desired relationship between the Western Latin and Catholic part of Christianity and its Eastern and Orthodox part. I say “desired” because, as we all know – despite the unexpected rapprochement between the popes and the ecumenical patriarchs since the advent of the Second Vatican Council – these two parts of the Christian world remain divided by a schism that has not yet been resolved. The Orthodox world, rich in an extraordinary tradition, is increasingly appreciated in the West, especially for its exceptional liturgical art – which skillfully serves our understanding of Christian cosmology – and its treasure of spiritual life. The mystical practice of hesychasm, in particular, is a vein of growing interest in the West, from Gregory Palamas to Silouan the Athonite. The extraordinary preservation of the Christian tradition in the Orthodox world is a testimony of its attachment to the Spirit. It is common in Catholic circles interested in the ecumenical question to argue that the main factor explaining the rupture of Eucharistic communion between the Catholic Church and the Orthodox Church is a divergence in their respective conceptions of ecclesiology, that is, the theology of the Church. However, certain elements of Trinitarian theology, highlighted in the Filioque dispute, were also decisive in the schism.   Divergent understandings of the Church While the development of divergent understandings of the Church remains fundamental, a brief analysis can shed light on the relationship between the Church’s movement towards synodality under the leadership of Pope Francis and the continuation of ecumenical dialogue. The Catholic Church is characterized by a radical conception of papal authority, whose jurisdiction extends to the whole universal Church. In the 19th century, on the occasion of the First Vatican Council and in the context of the loss of the Papal States, the dogma of papal infallibility was proclaimed. For Catholics, the pope is thus prevented from error on matters of dogma and morals when speaking ex cathedra in his ordinary and extraordinary power. The proclamation of the dogma of papal infallibility by the Council Fathers was the culmination of a doctrinal development in the Catholic Church concerning the authority of the popes, which derives from the words of Jesus: "And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it" (Matthew 16:18). The Orthodox Church has a different interpretation of these words. Indeed, for the Orthodox, the privilege accorded to the Bishop of Rome is understood as a primacy of honour, granting him a status of primus inter pares – first among equals – rather than a universal jurisdiction extending beyond the limits of his patriarchate. The division that gradually arose between these two parts of Christianity is directly related to this disagreement. Because of the schism, it is the Ecumenical Patriarch of Constantinople, the New Rome, who theoretically enjoys this primacy. Interestingly, however, the paths taken since the schism of 1054 in the Catholic Church and the Orthodox Church have been in a sense marked by the radicalization of these two contradictory dispositions. Indeed, the Western Middle Ages were marked by a slow process of centralization of ecclesiastical authority – and sometimes even civil authority, with the excesses that we know – around the figure of the pope, a process that reached a peak in the period between the First and Second Vatican Councils. In contrast, the development of the Church in the Orthodox world has been characterized by a multiplication of jurisdictions, whose often difficult relationships do not always find obvious solutions in the context of a collegial ecclesiology. And even if it is tempting to separate these ecclesiological considerations from the content of the faith, it remains important to see things in their unity.   The breath of the council: synodality and ecumenism The experience of the Second Vatican Council, which is part of a long and uninterrupted conciliar tradition, encouraged Pope Paul VI to establish in 1965 the Synod of Bishops, a permanent collegial institution to support the Supreme Pontiff in the exercise of the Petrine ministry. The Synod does not substitute for the authority of the pope and cannot act in a way that contradicts it; rather, it introduces a measure of collegiality into the government of the Church. The notion of a synod is not new; this decision-making mechanism is deeply rooted in the general history of Christianity. And it is interesting to note that the term "synod" is also used in Orthodoxy to designate a body composed of bishops exercising a number of major functions in several of the various autocephalous churches. In this sense, the establishment of the Synod of Bishops in the wake of the last council cannot be described as an innovation of Pope Saint Paul VI but rather as a further opening up of papal authority to collegiality, rooted in ecclesial tradition. Under Pope Francis' leadership, the Church has undertaken a reforming process to emphasize the importance of the synodal process, arousing enthusiasm among some for whom the implementation of long-anticipated reforms has been slowed or hindered by an excessive centralization of decision-making processes around the Roman Curia. Less has been said recently about the potential effects of the movement towards synodality on the ecumenical process, which began especially with Pope Saint Paul VI and the Ecumenical Patriarch Athenagoras I in the wake of Vatican Council II. It is well known that Pope Francis has attached great importance to the renewal of this process, together with Patriarch Bartholomew I of Constantinople. Having simply presented himself at his election as the new Bishop of Rome – which in no way calls into question the pontifical authority – Pope Francis shares with Bartholomew I a strong ecological commitment, which has often brought them together. The Synod – which Pope Francis promises to revitalize through the synod on synodality which recently opened – as a tool of collegiality, could be welcomed as a relaxation of the centrality proper to Catholic ecclesiology, which is badly received in the Christian East.   A cautious and patient approach The Synod is a promising instrument for collegiality in the Church, and it can support the ecumenical process, provided that its meaning and foundations are understood in the light of the tradition in which its renewal takes place. Indeed, the Synod cannot be understood as a break with Catholic ecclesiology without running certain risks. Looking at the Orthodox world after the schism, we are forced to note the realities of jurisdictional division, the inclination to politicize ecclesial life and the permanence of a national feeling that is sometimes excessive in certain communities. As one example, consider the break in Eucharistic communion that occurred in 2018 between the Patriarchate of Moscow and the Ecumenical Patriarch over a jurisdictional dispute regarding the Orthodox Church in Ukraine. One might be tempted to argue that this situation, which is not new, is somehow related to such a collegial and decentralized conception of the Church that it can, in some cases, lose sight of the truly universal character of the community of believers. Interpreting the movement towards synodality as a rupture thus carries with it a potential risk of fragmentation.   A Synod that supports the Petrine ministry Although pontifical supremacy has given rise to abuses in the Church, it has at the same time been the instrument and vehicle of her unity on the institutional level, and also the motor of an organic and continuous doctrinal development by which, sustained in her being by the Spirit, she pursues her path by rejecting what is superficial and maintaining what is essential. Thus, by the grace of God, the Catholic Church remains in her unity skillfully attached to the elementary moral and spiritual truths, which are sometimes set aside elsewhere. Here, doctrine unfolds naturally, like a tree whose growth continues without discontinuity or contradiction. To perceive the movement towards synodality as an alteration of the authority of the pope – and, moreover, of the council – would thus entail the risk of losing our bearings, or else of becoming stagnant. We are called, as Catholics, to enter into this process with confidence, and to participate – each according to his or her state of life, each according to his or her particular charisms – in Christ's discernment for His Bride, the Church. In this way, we will be able to welcome this opportunity to participate in a different way in the life of the Church and, as far as possible, in the reconciliation of the whole Body of Christ. In due course, we can seek to understand the conclusions of this process in the light of the whole of Christian Revelation and Tradition.