“Nicaea and the Church of the Third Millenium: Towards Catholic-Orthodox Unity”
Conference co-sponsored by IOTA and the Oecumenicum Institute for Ecumenical Studies, Angelicum
Rome, June 4-7, 2025

On the morning of Saturday, June 7th, the participants of the conference “Nicaea and the Church of the Third Millenium” convened in the Sala Clementina of the Apostolic Palace to meet Pope Leo XIV. The fact that Catholic and Orthodox prelates and scholars should meet in a room dedicated to the memory of Saint Clement could not have been more fitting. Clement, the third bishop of Rome was martyred in Chersonesus, the location of the presumed place of St. Vladimir’s baptism, which started the conversion of the Slavic people to Christianity, and Clement’s relics were brought to Rome from Crimea in the year 868 by none other than Cyril and Methodius, who wanted to receive the blessing of Pope Adrian of Rome for their mission of evangelization. Clement’s story, moving from Rome to Ukraine and then back to Rome, perfectly symbolizes the role played by the Roman see at the time of the undivided church of the first millennium, not just in promoting evangelizing efforts in the East, but also in shaping the Christian imagination.

In his short speech, Pope Leo mentioned the three themes of the conference, each of which marked one of the three days of the proceedings: the content of the Nicene faith, its synodal character which is so very relevant now that Catholics are rediscovering the synodal dimension of ecclesial life, and finally the question of the date of Easter – the one matter that most attracted the attention of the media, as the pontiff clearly stated his openness to agreeing on a joint date for its celebration. Yet, towards the end of his remarks, the pope also observed: “The unity for which Christians long will not be primarily the fruit of our own efforts, nor will it be realized through any preconceived model or blueprint. Rather, unity will be a gift received ‘as Christ wills and by the means that he wills’”. These last few words were a citation from the “Prayer for Unity” by Paul Couturier (1881–1953), a French priest who played an important role in the establishment of the Week for Christian Unity. Couturier’s personal history shaped his interreligious and ecumenical sensitivity – he was of Jewish descent and had been raised in an Islamic setting in Algeria – but what spurred his decision to devote himself to the cause of Christian unity was his work among the Russian Orthodox refugees who flooded Paris in the early 1920s. Fascinated by Orthodox theology and spirituality, Couturier would write in his spiritual testament that the Holy Spirit had made him painfully aware of the divisions between Christians, and that only the Spirit could heal these divisions. Indeed, it is the Spirit whom the pope invoked at the end of his speech with the words of the Eastern prayer “O Heavenly King” – that Spirit who was certainly present at Nicaea, even if it was only the later council of Constantinople that would affirm the Spirit’s full divinity.

The papal audience was certainly a highlight of the conference, but the three and a half days of lectures, panels, and discussions brought together an extraordinary community of scholars from the Roman Catholic and Eastern Orthodox traditions, as well as from the non-Chalcedonian Orthodox churches, the Anglican communion, and numerous Protestant groups. While the focus of the event was on Catholic and Orthodox dialogue, the contributions of many speakers from the ancient churches of Syria and Egypt, as well as from the churches that emerged after the Reformation, demonstrated the central role of the doctrines of the early councils in shaping the Christian theological imagination. The very manner of reception of these doctrines is often a factor determining the institutional and ecclesial character of individual churches, some of which may not accept the definitions of all early councils, but may nonetheless feel bound to preserve the Christological and Trinitarian consensus of the fourth and fifth centuries. The pan-ecclesial character of the conference – not just in virtue of the co-operation between IOTA and the Pontifical University of Saint Thomas Aquinas, but thanks to the genuine commitment of all participants to an ecumenical vision rooted in a common faith – is what set this event apart from other conferences devoted to Nicaea that are taking place in this anniversary year. The three keynote addresses by Cardinal Koch, the representative of the Ecumenical Patriarchate Metropolitan Job of Pisidia, and former Archbishop of Canterbury Rowan Williams, while reflecting the distinctive background and theological sensitivity of the speakers, agreed in calling for a renewed appreciation of the legacy of Nicaea, and in invoking its relevance for our joint pilgrimage towards ecclesial unity. Dr. Williams, in particular, talked of the Nicene grammar of creation, the uncovering of the Christocentric character of the natural order that challenges us to overcome discord and strife to build our communal home in a time of conflict and environmental devastation.

While the discussions of the first day revolved around classical questions of Christology and Trinitarian theology, on the second day the lectures and panels moved on to discuss the issue of synodality, which in recent years – thanks to Pope Francis’s commitment to ecclesial renewal – has acquired a new importance for Roman Catholics. The plenary speakers addressed the relationship between synodality and primacy in the light of Nicaea; the second morning panel, in particular, centered on the important document “The Bishop of Rome: Primacy and Synodality in the Ecumenical Dialogues and in the Responses to the Encyclical Ut unum sint,” published in 2024 by the Dicastery for Promoting Christian Unity. Significant contributions were offered by Fr. Hyacinthe Destivelle, OP, director of the Institute for Ecumenical Studies at the Angelicum, and George Demacopoulos, co-founding director of the Orthodox Studies Christian Center at Fordham University in New York. On the third day, after the conference participants returned from the papal audience, the discussion moved on to the question of the date of Easter, as well as to other methodological and pastoral implications of the council’s legacy.

An aspect of this conference the participants will certainly remember with fondness – apart from the wonderful opportunity to socialize over food and drink in the Angelicum gardens – were the moments of prayer that opened and ended every day of the proceedings. After the opening day’s ecumenical service and the performance of the Dominican choir of the Angelicum, over the following three days the university’s Aula Magna was filled with the singing of the Coptic Orthodox choir of Rome, the choir of the Romanian Orthodox Diocese of Italy, and finally the choir of the Ukrainian Pontifical College of Saint Josaphat. In these brief pauses of reflection, listening to different musical expressions of the same faith by members of churches that are still not in communion with each other, everyone was reminded of the fact that as Christians, we are all walking towards the same mystery even if we follow different paths.

Thomas Cattoi
William and Barbara Moran Chair in Early Christian Theology and Interreligious Relations
Pontifical University of Saint Thomas Aquinas, Rome