On the occasion of the symposium "Nicaea and the Church of the Third Millennium: Towards Catholic-Orthodox Unity," held at the Pontifical University of St. Thomas Aquinas, Pope Leo XIV called for a renewed commitment to ecumenical engagement between Catholics and Orthodox Christians, drawing inspiration from the Council of Nicaea as a foundation for a common synodal path. Before representatives of Eastern and Western Churches, he emphasized that Nicaea is not just a past event, but a compass guiding Christians towards full visible unity, inviting them to "see the points that still separate us in a new light" and to move towards the restoration of communion. This speech is part of the 1700th anniversary celebration of the council, marked as a decisive step for the common profession of faith and the revitalization of an authentic ecumenical dialogue.

Peace be with you! Eminences, Excellencies, Ladies and Gentlemen Professors, Dear Brothers and Sisters in Christ, I warmly welcome all of you participating in the Symposium "Nicaea and the Church of the Third Millennium: Towards Catholic-Orthodox Unity," organized jointly by Ecumenicum – the Institute of Ecumenical Studies of the Angelicum – and the International Orthodox Theological Association. I particularly greet the representatives of the Orthodox and Eastern Orthodox Churches, many of whom honored me with their presence at the inauguration mass of my Pontificate.

Before continuing my official speech, I would like to apologize for my slight delay and ask you to be patient with me. I have not yet been in office for a month (laughter), so I have much to learn. But I am very happy to be among you this morning.

I am pleased to see that the Symposium is resolutely focused on the future. The Council of Nicaea is not only an event of the past but a compass that must continue to guide us towards the full visible unity of Christians. The first ecumenical council is the foundation of the common path that Catholics and Orthodox have undertaken together since the Second Vatican Council. For the Eastern Churches commemorating its celebration in their liturgical calendar, the Council of Nicaea is not just another council or the first in a series, but the council par excellence, which promulgated the norm of the Christian faith, the creed of the "318 Fathers."

The three themes of your Symposium are particularly relevant to our ecumenical journey. First, the faith of Nicaea. As the International Theological Commission noted in its recent document for the 1700th anniversary of Nicaea, the year 2025 represents "an invaluable opportunity to emphasize that what we have in common is much stronger, quantitatively and qualitatively, than what divides us. Together, we believe in the Trinitarian God, in Christ true man and true God, and in salvation through Jesus Christ, according to the Scriptures read in the Church and under the motion of the Holy Spirit. Together, we believe in the Church, in baptism, in the resurrection of the dead, and in eternal life." (cf. Jesus Christ, Son of God, Saviour, n. 43). I am convinced that by returning to the Council of Nicaea and drawing together from this common source, we will be able to see the points that still separate us in a new light. Through theological dialogue and with God's help, we will come to better understand the mystery that unites us. By celebrating this faith of Nicaea together and proclaiming it together, we will also move towards the restoration of full communion among us.

The second theme of your symposium is synodality. The Council of Nicaea inaugurated a synodal path that the Church must follow to address theological and canonical issues at the universal level. The contribution of the delegated brothers of the Eastern and Western Churches to the recent Synod on synodality, held here at the Vatican, was a valuable stimulus for greater reflection on the nature and practice of synodality. The Final Document of the Synod noted that "ecumenical dialogue is fundamental to developing our understanding of synodality and the unity of the Church" and went on to encourage the development of "ecumenical synodal practices, including forms of consultation and discernment on urgent and common interest issues" (For a Synodal Church: Communion, Participation, Mission, n. 138). I hope that the preparation and common commemoration of the 1700th anniversary of the Council of Nicaea will be a providential opportunity "to deepen and profess together our faith in Christ and to practice forms of synodality among Christians of all traditions" (cf. ibid., n. 139).

The Symposium has a third theme related to the date of Easter. As we know, one of the objectives of the Council of Nicaea was to establish a common date for Easter to express the unity of the Church across the whole oikoumene. Unfortunately, calendar differences no longer allow Christians to celebrate together the most important feast of the liturgical year, creating pastoral problems within communities, dividing families, and undermining the credibility of our witness to the Gospel. Several concrete solutions have been proposed that, while respecting the principle of Nicaea, would allow Christians to celebrate together the "Feast of Feasts." In this year when all Christians celebrated Easter on the same day, I reaffirm the Catholic Church's openness to seeking an ecumenical solution that promotes a common celebration of the resurrection of the Lord and thus gives greater missionary strength to our preaching of the "name of Jesus and the salvation that arises from faith in the salvific truth of the Gospel" (Address to the General Assembly of the Pontifical Missionary Works, May 22, 2025).

Brothers and sisters, on the eve of Pentecost, let us remember that the unity Christians aspire to will not first be the fruit of our efforts nor will it be realized through a pre-conceived model or plan. Unity will rather be a gift received "as Christ wants it and by the means he wants," through the action of the Holy Spirit. And now I invite you all to stand so that we can pray together to implore from the Spirit the gift of unity. The prayer I will recite implores the unity of the Spirit in a prayer taken from the Eastern tradition:

"Heavenly King, Comforter, Spirit of Truth, You who are everywhere present and fill all things; Treasure of good and giver of life, Come and dwell in us, and cleanse us from all impurity, And save our souls, you who are goodness."

Amen. May the Lord be with you. May the blessing of Almighty God, the Father, the Son, and the Holy Spirit, descend upon you and remain with you always. Amen. Thank you very much.