LECTURE AT THE INTERNATIONAL CONFERENCE
"NICEA AND THE CHURCH OF THE THIRD MILLENNIUM:
TOWARDS CATHOLIC-ORTHODOX UNITY"
ROME, 4 JUNE 2025
THE 1700TH ANNIVERSARY OF THE COUNCIL OF NICAEA:
AN ECUMENICAL OPPORTUNITY AND CHALLENGE
Kurt Cardinal Koch
The ecumenical movement is not simply a royal road, broadly organised and leading directly to a good future. Alongside the main roads, it also has side roads, detours, and byways. Of course, it also recognises particularly favourable occasions that promise a hopeful future. The 1700th anniversary of the First Ecumenical Council in the history of the Church, held in Nicaea in 325, will undoubtedly be a significant ecumenical moment for the whole of Christendom in 2025. The commemoration of this important event carries significant ecumenical prospects, specifically in three respects.
1. Unity in the apostolic faith
On the occasion of Pope Francis’ visit to Ecumenical Patriarch Bartholomew I in Constantinople for the feast of St Andrew, the patron saint of this Patriarchate, in 2014, he spoke these moving words: “I want to assure each of you that the Catholic Church, in order to achieve the longed-for goal of full unity, does not intend to impose any requirement other than that of professing the common faith.” He went on to add: “The only thing that the Catholic Church desires, and that I, as Bishop of Rome, <the Church that presides in charity>, aspire to, is communion with the Orthodox Churches”.[1]
a) Binding profession of faith
With this assurance, Pope Francis expressed that ecumenism is, at its heart, a matter of faith. The restoration of the unity of the Church requires agreement on the essential content of the Christian faith — not only among the churches and ecclesial communities of today, but also in continuity with the Church of Tradition and, above all, with its apostolic origins. The unity of the Church to be regained through ecumenical endeavour — as a community living in fidelity to the Gospel and the Apostolic Faith — can never be anything other than the unity in the Apostolic Faith, which is given and entrusted to every new member of the Body of Christ in Baptism.
The ecumenical significance of the Council of Nicaea therefore lies primarily in the “Declaration of the 318 Fathers”, in which the bishops gathered at Nicaea confessed their faith in the “one Lord Jesus Christ, the Son of God”, and expressed this with the Greek term “homoousios”, meaning that Jesus Christ, as the Son of God, is of the same substance as the Father, and therefore “God from God, Light from Light, true God from true God, begotten, not made.”[2] The Council Fathers thus set out their decisive conviction of faith that Jesus Christ belongs to the realm of God and not to that of creation, and is therefore truly the only Son of God.
In order to understand why the Council of Nicaea marked such a significant milestone, it is necessary to briefly recall its historical background. At the beginning of the fourth century, the question of who Jesus Christ is had become a problem case within Christianity. The debate centred primarily on the question of how the Christian belief in Jesus Christ as the Son of God could be reconciled with the equally Christian belief in the one and only God, in accordance with the monotheistic creed. This challenge was provoked above all by the Alexandrian presbyter Arius, who advocated a strict monotheism in line with the philosophical thinking of the time, which was founded on the conviction that there can be only one God.[3] In his view, Jesus Christ could not therefore be the Son of God in the true sense of the term, but merely an intermediary being through whom God acts in the creation of the world and in his dealings with humanity.
The bishops at Nicaea rejected the concept of a strict philosophical monotheism promoted by Arius and declared in the “Letter of the Synod of Nicaea to the Egyptians” that they had condemned Arius’ “doctrine hostile to the faith” with an anathema.[4] On a positive note, in the “Declaration of the 318 Fathers”, they professed their faith in Jesus Christ as the Son of the same substance as the Father. The Creed of Nicaea therefore represents an important, though not yet complete, stage on the path to the Great Creed of Constantinople. This is because the Council of Nicaea defined the faith in Jesus Christ but only referred to faith in the Holy Spirit in general terms: “and in the Holy Spirit.” It was the Council of Constantinople that first defined the content of the profession of faith in the Holy Spirit, thereby enabling the formulation of the dogma of the Divine Trinity in the specifically Christian form of monotheism.
In the Nicene-Constantinopolitan Creed, we find the foundation of the faith common to all Christians. While the Apostles’ Creed, widely used in the Western Church, has not gained liturgical acceptance in the Eastern churches, the Creed of Nicaea and Constantinople has been unanimously embraced by Orthodox, Catholic, and Protestant Christianity. As the Protestant ecumenist Wolfhart Pannenberg has emphasised, it is therefore “associated with a claim to universal church validity and was also received by the early church as binding for all Christians.” [5] It thus represents the strongest ecumenical bond of the Christian faith.
This important ecumenical significance is also due to the fact that the Council of Nicaea took place at a time when Christianity had not yet been divided by the many subsequent schisms. Its creed is therefore shared by all Christian churches and ecclesial communities, uniting them in a common confession to this day. Its ecumenical importance cannot be underestimated. It is thus to be wished and hoped that the 1700th anniversary of the Council of Nicaea will be celebrated by the whole of Christianity in a spirit of ecumenism, and that its Christological creed will be renewed in ecumenical unity.
b) Lasting relevance of the confession
The Nicene-Constantinopolitan Creed is recited every Sunday during the liturgies of various churches. It thus provides an excellent opportunity for the faithful to continually profess the faith of the early Church. But what is the status of this creed in the churches and in ecumenism today?
If we look with genuine openness at today’s world of faith in our latitudes, we must recognise that we find ourselves once again in a situation similar to that of the fourth century, insofar as there is a strong resurgence of Arian tendencies. For example, in the 1970s, a Catholic theologian judged the early Church councils as follows: “The mythical ideas of that time of a prematurely otherworldly heavenly existence of a being derived from God, of a ‘god story’ between two (or even three) divine beings, can no longer be ours.”[6] From this, he concluded: “The one-God belief, adopted by Israel and shared with Islam, must not be abandoned in any doctrine of the Trinity. There is no other God besides God!”[7] While the intention behind such a claim – namely, the promotion of interreligious dialogue – is certainly commendable, the path proves to be a detour, since one cannot gain greater acceptance of the Christian faith in interreligious dialogue by excluding or even rejecting its heart, namely the belief in the Trinity.
It is therefore unsurprising that such a subordinated Christology has also found its way into the faith consciousness of today’s Church. Cardinal Joseph Ratzinger described this renewed Arianism succinctly with the formula: “Jesus yes – Christ no” or “Jesus yes – Son of God no.”[8] This phenomenon is particularly evident in the fact that many Christians today are certainly moved by the human and historical dimensions of Jesus of Nazareth, yet find it very difficult to profess the faith that Jesus of Nazareth is the only begotten Son of the heavenly Father, who is present among us as the risen One, and in this respect, the Church’s faith in Christ.
Even within the Church and in ecumenical dialogue, it often seems almost impossible today to recognise the face of God in the man Jesus of Nazareth and to confess him as the Son of God, rather than merely viewing him as a human being — albeit a particularly good and remarkable one. Yet this effectively reduces the sonship of Jesus Christ to the level of a holy man, as the Protestant theologian Eberhard Jüngel incisively observed: “A Christology that merely highlights the exemplary nature of Jesus… reduces the significance of Jesus Christ to that of a saint who is also capable of sacrificing his life, but who can, at most, appeal through the example of his life’s sacrifice without being able to effectively change the life of humanity. The life of humanity is only truly changed by transforming humanity’s relationship with God”.[9]
That humanity’s relationship with God can be changed and in fact has been effectively changed — this is precisely what the Christian faith confesses about the Christ event, as attested by the Council of Nicaea in 325 and the Council of Constantinople in 381. The Christian faith stands or falls with this fundamental Christological confession. For if Jesus — as quite a few Christians today assume — were merely a man who lived two thousand years ago, then he would have irrevocably receded into the past, and only our own memory could, more or less vividly, recall him into our present. In that case, however, Jesus Christ could not be the only Son of God, in whom God himself is present with us human beings.
Only if Jesus was not only a man two thousand years ago, but is also alive today, can we experience his presence and can we experience through Jesus Christ who and how God is. For those who come into contact with the man Jesus come into contact with the living God himself, who has shown us his face in his only Son. This shed light on the deepest reason why the Christological dogma of the Church formulates the mystery of the incarnation in a classic way by saying of Jesus Christ that he is “perfect in Godhead and perfect in humanity” and that in him the two natures exist “unmixed, unmodified, undivided and unseparated”.[10]
In light of the current situation of faith in the churches and within the ecumenical movement, the enduring significance of the Council of Nicaea and its culmination in the Council of Constantinople becomes newly evident. The study of these councils is therefore not only of historical interest; rather, their Christological confession possesses lasting relevance for the Church and ecumenism also today. Revitalising the confession of Jesus Christ — to learn once more to see him in all his greatness and beauty — is an urgent task of our time, one that must be undertaken in ecumenical fellowship. For the heart of Christian ecumenism lies in the common conversion of all Christians and churches to Jesus Christ, in whom the unity sought in ecumenical efforts is already preordained. Christian ecumenism can only move forward credibly if Christians together return to the source of faith, which can only be found in Jesus Christ, as the Fathers of the Council of Nicaea confessed. Christian ecumenism must be understood and realised as an ecumenism of Christ, as expressed in the motto of Pope Leo XIV’s pontificate: “In illo uno unum”. The more we Christians, in our different churches and ecclesial communities, unite in Christ and become one in him, the more we shall also be one with one another.
2. Synodal consultation and decision
The Creed of the Council of Nicaea is not merely the result of theological reflection, but the expression of a joint — more precisely, synodal — struggle of bishops for an orthodox and doxologically appropriate formulation of the Christian faith. From an ecumenical perspective, this council is also of great significance, as it documents the manner in which the then-heated controversy over the orthodox confession of Christ was debated and resolved in synodal fashion. Of the approximately 1,800 bishops of the ancient Church who were invited, it is believed that 318 took part in the council. The Church writer Eusebius, himself a participant at the Council of Nicaea, viewed it as a new Pentecost and emphasised that the foremost servants of God, “from all the churches throughout Europe, Africa, and Asia,” were gathered together at this council.[11]
The Council of Nicaea can therefore be seen as the beginning of the synodal way of decision-making and decision-taking in the Church as a whole. The word itself indicates this, as “synod” is composed of the Greek terms “hodos” (= way) and “syn” (= with) and expresses the fact that a way is travelled together. In the Christian understanding of faith, the word refers to the common path of people who believe in Jesus Christ, who revealed himself as “the way”, more precisely as “the way, the truth and the life” (John 14:6). Therefore, Christian religion was originally called “the way” and Christians who followed Christ as the way were called “followers of the way” (Acts 9:2). In this sense, the Doctor of the Church St John Chrysostom was able to explain that “church” is a name “that stands for a common way” and that church and synod are “synonyms”.[12]
The 1700th anniversary of the Council of Nicaea should therefore also be regarded as an invitation and a challenge to learn from history and to deepen the synodal idea today in ecumenical fellowship, to anchor it in Church life and to make it fruitful in ecumenical dialogues. For ecumenism, too, can only make progress on the way to regaining the Church’s unity if it is travelled together and thus in a synodal manner. Conversely, today’s revitalisation of the Church’s synodal dimension can itself be enriched through ecumenical encounters.[13]
(The importance of synodality in ecumenical endeavours has been impressively demonstrated in recent years by two significant theological-ecumenical documents. A few years ago, the Commission on Faith and Order of the World Council of Churches published the study The Church: Towards a Common Vision, which seeks a multilateral and ecumenical understanding of the nature, purpose, and mission of the Church. In this study, an ecclesiological statement is made that is shared ecumenically: “The whole Church is synodal/conciliar at all levels of Church life — local, regional, and universal — under the guidance of the Holy Spirit. The characteristic of synodality reflects the mystery of the Trinitarian life of God, and the structures of the Church give expression to this characteristic in order to realise the life of communion as communion.”[14] This view is likewise affirmed by the International Theological Commission in its document “Synodality in the Life and Mission of the Church”. In this text, it is joyfully noted that ecumenical dialogue has advanced to the point of recognising in synodality a “revelatory dimension of the nature of the Church”, insofar as it concerns an understanding of the “concept of the Church as koinonia”, “which is realised in each local church and in its relationship with other churches, through specific structures and synodal processes”.[15] In both documents, the fundamental interdependence between synodality and ecumenism becomes evident: just as the ecumenical path is synodal, so too must the synodal path be ecumenical.)
Since synodality has been developed and continues to unfold in different ways in various churches and ecclesial communities, there is much to learn from one another through ecumenical dialogues. This has been demonstrated by the International Ecumenical Symposia on Concepts and Experiences of Synodality in the Christian Churches in the East and West, organised by the Institute for Ecumenical Studies at the Pontifical University of St. Thomas Aquinas under the titles “Listening to the East” and “Listening to the West,” in preparation for the Synod of Bishops in the Catholic Church.[16] These symposia have powerfully documented that the Catholic Church can be enriched in the revitalisation of a synodal way of life by the experiences and theological reflections of other churches.
This applies especially to the Catholic-Orthodox dialogue, in which the important document “Ecclesiological and Canonical Consequences of the Sacramental Nature of the Church: Ecclesial Communion, Conciliarity and Authority” was adopted at the plenary assembly in Ravenna in 2007.[17]
This important document expresses the twofold theological conviction that synodality and primacy are mutually dependent, in the sense that there can be no primacy without synodality, and no synodality without primacy, and that this interdependence must be realised at all levels of the Church — local, regional, and universal. This document can be regarded as a milestone, upon which two further documents have been developed and published: in Chieti in 2016, “Synodality and Primacy in the First Millennium: Towards a Common Understanding in the Service of the Unity of the Church”, and in Alexandria in 2023, “Primacy and Synodality in the Second Millennium and Today”.[18]
The Catholic Church has learned a great deal from this ecumenical dialogue in embracing a synodal way of life. On the occasion of the commemoration of the fiftieth anniversary of the establishment of the Synod of Bishops by Pope Paul VI, Pope Francis emphasised that both the practice and the reflection on synodality must also be carried out from an ecumenical perspective within the Catholic Church. He affirmed that to deepen and resolutely pursue the path of synodality “is what God expects of the Church of the third millennium”, and linked this to his conviction that the effort to build a synodal Church is “rich in implications for ecumenism”.[19] And with regard to his Petrine ministry, he emphasised that a “careful study of how the principle of synodality and the ministry of the one who presides are expressed in the life of the Church” represents an important contribution to the ecumenical reconciliation of the churches.[20] That Pope Leo XIV would continue on this path was already made clear in his first address following the election, in which he gave the assurance: “We want to be a synodal Church.”[21]
3. The crucial question of the date of Easter
The Council of Nicaea is also of particular importance from an ecumenical perspective because, in addition to the Creed, it addressed canonical and disciplinary matters. These are outlined in twenty canons that deal with issues such as jurisdictional conflicts, cases of apostasy, and matters concerning the clergy. The most significant pastoral question was that of the date of Easter. This issue reveals that the date of Easter was already a point of contention in the early Church, and that Christians in different regions celebrated it on different days.[22] Christians, especially in Asia Minor, celebrated Easter on the 14th of Nisan, in parallel with the Jewish Passover, and were therefore called “Quartodecimans.” In contrast, Christians in Syria and Mesopotamia celebrated Easter on the Sunday following the Jewish Passover and were known as “Protopaschists.”
In view of this situation, it is to the credit of the Council of Nicaea that it established a uniform regulation, which it articulated in its “Letter of the Synod of Nicaea to the Egyptians” with the words: “All our brothers and sisters in the East who have hitherto kept Easter with the Jews will henceforth celebrate the Passover in accordance with the Romans, with you, and with all of us who, from ancient times, have observed it together with you.”[23] With this decision, the Council first established that Easter would be celebrated on the Sunday following the first full moon after the spring equinox. Secondly, it decreed that the exact date of Easter should no longer be determined by the Jewish calendar, and that the Christian celebration of Easter should therefore always take place after the Jewish Passover.
A new situation arose in the history of Christianity when Pope Gregory XIII introduced a major calendar reform in the 16th century, establishing the Gregorian calendar, named after him. According to this calendar, Easter is celebrated on the Sunday following the first full moon in spring. To this day, the churches of the West continue to calculate the date of Easter according to the Gregorian calendar. In contrast, the churches of the East largely continue to celebrate according to the Julian calendar, named after Gaius Julius Caesar, who reformed the Roman system of reckoning time in 46 BC. This Julian calendar remained in use throughout the Church until the Gregorian reform.
In the meantime, various proposals have been discussed in order to overcome the differences in the dating of Easter and to establish a common date for its celebration.[24] As far as the Catholic Church is concerned, it had already expressed its position at the Second Vatican Council in an appendix to the Constitution on the Sacred Liturgy Sacrosanctum Concilium, promulgated in 1963, declaring its openness to “assign Easter to a particular Sunday in the Gregorian calendar,” provided that “those whom it may concern, , especially the brethren who are not in communion with the Apostolic See, give their assent.”[25] With the same openness towards finding a common date for the celebration of Easter — on the condition that all Christian churches reach an agreement — Pope Francis has repeatedly affirmed: “The Catholic Church is ready to accept the date that everyone wants: a date of unity.”[26]
The 1700th anniversary of the Council of Nicaea presents a unique opportunity to revisit this question, especially since, in 2025, the churches of East and West could once again celebrate Easter on the same day, 20 April. It is therefore understandable the desire to renew efforts to determine a common date for Easter in a spirit of ecumenical fellowship, and to reconsider the then Council’s decision in light of today’s circumstances. The guiding principle must be to seek a common date without causing new tensions or divisions within the ecumenical community.
The endeavour to find a common date for Easter is an important pastoral concern, particularly for families of different denominations and in light of the increasing mobility of people today. Above all, a shared celebration of Easter would bear more credible witness to the profound conviction of the Christian faith that Easter is not only the oldest, but also the central and most important feast of Christianity.
To summarise, the ecumenical significance of the Council of Nicaea lies in the renewal and deepening of its creed, the revitalisation of a synodal way of life within the various churches, and the recovery of a common date for the celebration of Easter. If these concerns can be resolutely pursued, the 1700th anniversary of the Council of Nicaea — itself a milestone in church history — could become a significant ecumenical moment, one for which the ecumenical community may rightly give thanks.
[1] Francis, Address during the Divine Liturgy in the Patriarchal Church of St. George in Istanbul on 30 November 2014.
[2] Erklärung der 318 Väter, in: Dekrete der Ökumenischen Konzilien. Hrsg. von J. Wohlmuth. Band 1: Konzilien des ersten Jahrtausends (Paderborn 2002) 5.
[3] Vgl. Th. Böhm, Die Theologie des Arius, in: U. Heil und J.-H. Tück (Hrsg.), Nizäa – Das erste Konzil. Historische, theologische und ökumenische Perspektiven (Freiburg i. Br. 2025) 111-126.
[4] Brief der Synode von Nizäa an die Ägypter, in: Dekrete der Ökumenischen Konzilien. Hrsg. von J. Wohlmuth. Band 1: Konzilien des ersten Jahrtausends (Paderborn2002) 16.
[5] W. Pannenberg, Die Bedeutung des Bekenntnisses von Nicaea-Konstantinopel für den ökumenischen Dialog heute, in: Ders., Beiträge zur Systematischen Theologie. Band 3: Kirche und Ökumene (Göttingen 2000) 194-2004, zit. 197.
[6] H. Küng, Christ sein (München 1974) 436.
[7] Ebda. 467.
[8] J. Kardinal Ratzinger, Jesus Christus heute, in: Ders., Ein neues Lied für den Herrn. Christusglaube und Liturgie in der Gegenwart (Freiburg i. Br. 1995) 15-45, zit. 40.
[9] E. Jüngel, Das Opfer Jesu Christi als sacramentum und exemplum. Was bedeutet das Opfer Jesu Christi für den Beitrag der Kirchen zur Lebensbewältigung und Lebensgestaltung? in: Ders., Wertlose Wahrheit. Zur Identität und Relevanz des christlichen Glaubens = Theologische Erörterungen III (München 1990) 251-282, zit. 267.
[10] J. Neuner / H. Roos, Der Glaube der Kirche in den Urkunden der Lehrverkündigung (Regensburg 1971) Nr. 178.
[11] Eusebius, Vita Const. III, 7.
[12] J. Chrysostomos, Explicatio in Ps 149, in: PG 55, 493.
[13] Vgl. K. Kardinal Koch, Synodalität in der Katholischen Kirche in ökumenischer Perspektive. Papst und Bischöfe. Konzilien und Synoden, in: M. Graulich / J. Rahner (Hrsg.), Synodalität in der katholischen Kirche. Die Studie der Internationalen theologischen Kommission im Diskurs (Freiburg i. Br. 2020) 220-242.
[14] Die Kirche. Auf dem Weg zu einer gemeinsamen Vision. Eine Studie der Kommission für Glauben und Kirchenverfassung des Ökumenischen Rates der Kirchen (ÖRK) (Paderborn 2015).
[15] Internationale Theologische Kommission, Die Synodalität in Leben und Sendung der Kirche, Nr. 116.
[16] Listening to the East, Synodality in the Eastern and Oriental Orthodox Traditions. Edited by Institute für Eumenical Studies of the Angelicum. Pro Oriente Foundation = Collana Ut unum sint 4 (Città del Vaticano 2023); Listening to the West. Synodality in the Western Ecclesial Traditions. Edited by Institute for Ecumenical Studies of the Angelicum = Collana Ut unun sint 7 (Città del Vaticano 2024).
[17] Dokumentiert in: J. Oeldemann, F. Nüssel, U. Swarat, A. Vletsis (Hrsg.), Dokumente wachsender Übereinstimmung. Band 4: 2001-2010 (Paderborn – Leipzig 2012) 833-848.
[18] Dokumentiert in: J. Oeldemann, F. Nüssel, U. Swarat, A. Vletsis (Hrsg.), Dokumente wachsender Übereinstimmung. Band 5: 2011-2019 (Paderborn – Leipzig 2021) 1006-1014.
[19] Francis, Speech at the 50th anniversary celebration of the establishment of the Synod of Bishops on 17 October 2015.
[20] Francis, Address to the ecumenical delegation of the Patriarchate of Constantinople on 27 June 2015.
[21] Leo XIV, First Blessing “Urbi e Orbi” on 8 May 2025.
[22] Vgl. I. O. Lumma, Feiern im Rhythmus des Jahres. Eine kurze Einführung in christliche Zeitrechnung und Feste (Regensburg 2016), bes. 17-69: Der Kalender.
[23] Brief der Synode von Nizäa an die Ägypter, in: Dekrete der Ökumenischen Konzilien. Hrsg. von J. Wohlmuth. Band 1 Konzilien des Ersten Jahrtausends (Paderborn 2002) 16-19, zit. 19.
[24] Detaillierte Angaben dazu finden sich im Vortrag von B. J. Groen. Der beschwerliche Weg zu einem gemeinsamen Osterdatum, in: Nachrichtendienst Östliche Kirchen vom7. April 2021: Hintergrund.
[25] Appendix: Declaration of the Second Vatican Council on calendar reform.
[26] Francis, Homily at the 2nd Vespers of the 58th Week of Prayer for Christian Unity on 25 January 2025.