Pope Leo XIV urges Christians to move past theological disputes and rediscover the faith professed at the Council of Nicaea. The Pope released an apostolic letter, 'In unitate fidei,' linking the anniversary of the first ecumenical council to the Holy Year of 2025. The Nicene Creed is presented as a foundation for renewed Christian unity, emphasizing unity in diversity. The Pope calls for a common understanding and prayer to the Holy Spirit to achieve full communion among Christians. Restoring Christian unity is described as a spiritual challenge requiring repentance and conversion.
22 days ago
Pope Leo XIV released the apostolic letter In unitate fidei ("In the Unity of Faith") on November 23, 2025, coinciding with the solemnity of Christ the King.1 2 The document ties the 1,700th anniversary of the Council of Nicaea to the 2025 Holy Year themed "Christ our hope" and the pope's upcoming journey to Türkiye for ecumenical commemorations with Ecumenical Patriarch Bartholomew.1 2
The letter aims to renew enthusiasm for professing the Nicene-Constantinopolitan Creed, described as a shared Christian heritage needing fresh relevance.1 2
Leo XIV urges Christians to transcend "outdated theological controversies" that hinder unity, using the Nicene Creed as a foundation for full communion.1 2 He emphasizes "unity in legitimate diversity," likening it to the Trinity, and warns that unity without multiplicity leads to tyranny while multiplicity without unity causes fragmentation.1 2
Restoring visible unity enriches rather than impoverishes, presenting it as a spiritual challenge requiring repentance and conversion from all.1 2 Ecumenism, rooted in shared baptism and the Creed, fosters recognition of mutual brotherhood and advances global peace efforts.1 2
The Council of Nicaea in 325 addressed the Arian heresy questioning Christ's divinity, affirming him as "consubstantial with the Father" to uphold biblical monotheism and the Incarnation.1 2 Leo XIV clarifies that terms like "substance" clarified Scripture without replacing it with Greek philosophy, countering Arius's Hellenized errors.1 2
The Creed portrays a relational God who draws near, especially to the poor, revolutionizing pagan views of divinity.1 2 It also underscores Christ's full humanity, leading to human divinization—true fulfillment in God—as echoed by St. Athanasius.1 2
In times of war, injustice, disasters, and poverty, the Nicene Creed offers hope centered on Christ as Son of God who descended for salvation.1 2 The Holy Year's timing with Nicaea's anniversary is seen as providential, inviting Christians to transmit faith joyfully.1 2
Leo XIV laments modern indifference to God, partly due to Christians' inconsistent witness, and critiques portrayals of a vengeful deity over a merciful one.1 2
The Creed must permeate liturgy and life, prompting questions about personal faith reception and its impact on daily existence.1 2 It invites scrutiny of idols, treatment of creation as humanity's common home, and commitment to social justice.1 2
At its core is confessing Jesus as Lord, committing followers to his demanding path of love, including for enemies, as true witness to God's mercy in suffering.1 2
The letter ends with a prayer invoking the Holy Spirit as guide and unifier, thanking him for the Creed and seeking harmony to form one flock.1 2 Leo XIV calls for wisdom to embody Christ's oneness, enabling the world to believe.1 2
Explore the Catholic Church’s role in fostering Christian unity
The Catholic Church views the pursuit of Christian unity as a divine imperative rooted in Christ's prayer that "they may all be one" (Jn 17:21), a call echoed throughout her teachings and actions. This role is not merely diplomatic but theological, aiming for full visible communion in faith, sacraments, and apostolic governance, while acknowledging the real bonds already shared through baptism and common heritage. Drawing from the Second Vatican Council's Decree on Ecumenism (Unitatis Redintegratio), papal exhortations, and official documents, the Church positions herself as both a participant and a catalyst in the ecumenical movement, fostering unity through prayer, dialogue, renewal, and collaboration without compromising doctrinal truth.
The Church recognizes that divisions among Christians, beginning in the early centuries and intensifying through historical schisms, contradict Christ's will and scandalize the world by hindering the Gospel's proclamation. As the Second Vatican Council affirmed, Christ founded one Church, yet "many Christian communions present themselves to men as the true inheritors of Jesus Christ," differing in mind and ways as if Christ were divided. This reality prompted the Council to declare the restoration of unity as one of its principal concerns, rousing divided Christians to remorse and longing under the Holy Spirit's grace. The ecumenical movement, involving those who invoke the Triune God and confess Jesus as Lord, seeks a visible, universal Church to convert the world to the Gospel.
The Council traces these rifts to human failings on both sides but embraces separated brethren with respect, noting that those baptized in Christ share an imperfect communion with the Catholic Church. Elements like Scripture, grace, faith, hope, charity, and liturgical actions exist outside full communion, serving as means of salvation and drawing all back to Christ's one Church. Yet, full unity—confession of one faith, common worship, and fraternal harmony—requires overcoming obstacles through the ecumenical effort, which the Church solemnly pledged to advance. This commitment reflects the Church's self-understanding as the "all-embracing means of salvation," entrusted with the New Covenant's blessings via the apostolic college under Peter's successor.
The Church's approach to unity is guided by Catholic principles that emphasize conversion of heart, fidelity to apostolic tradition, and patient dialogue. Unity subsists in the Catholic Church, which can never lose it, but it must grow until all Christians are gathered in the one Eucharist. The ecumenical movement involves initiatives like avoiding uncharitable judgments, expert dialogues to deepen mutual understanding, cooperation in the common good, and common prayer where appropriate. These actions, undertaken prudently under bishops' guidance, promote justice, truth, and brotherly love, leading to renewal and reform within the Church herself.
Central to this is "spiritual ecumenism," the soul of the movement: a change of heart, holiness of life, and prayer for unity, especially Christ's prayer on the eve of his death. Catholics are encouraged to join separated brethren in prayer during special circumstances, as it expresses existing ties and obtains grace for unity. However, common worship (communicatio in sacris) is not indiscriminate; it must witness to Church unity and share in grace, decided by local authorities. The Church also stresses self-examination: her members must appraise needs for renewal to bear clearer witness, as failures in living the faith obscure her catholicity. Diversity in spirituality, rites, and theological expressions is welcomed, provided unity in essentials prevails and charity guides all.
Moreover, the Church acknowledges truly Christian endowments among separated brethren—riches of Christ, virtuous works, even martyrdom—as aids to edification, never contrary to genuine faith. Yet divisions prevent full catholicity, making ecumenical work essential for expressing the Church's wholeness. The Council commends growing Catholic participation, urging bishops to stimulate it prudently.
Successive popes have embodied and advanced this role, committing the Church irrevocably to the ecumenical path since Vatican II. Pope John Paul II, early in his pontificate, engaged the Secretariat for Promoting Christian Unity (now the Dicastery for Promoting Christian Unity), viewing it as symbolic of the Church's forward momentum toward unity. He emphasized assessing progress, straining forward in faith (Phil 3:13), and collaborating at every level in submission to the Holy Spirit. This included official dialogues, delegating observers to ecumenical meetings, and coordinating national efforts.
John Paul II repeatedly called for theological dialogue to resolve faith divisions, rooted in love and deepening the "faith delivered once for all to the saints." He highlighted koinonia (communion) as participation in the Triune God's life, foundational for discussing Church structure, diversity, Eucharist, and primacy. In addresses to ecumenical bodies, he praised multilateral dialogues on apostolic faith and Church unity, urging agreement on "one body... one faith, one baptism" (Eph 4:4-6). Pope Paul VI stressed charity as the connecting fabric of ecclesial unity, educating the faithful in mutual love to counter pluralism's dangers, which must not contradict Christianity's substantial unity.
Pope Benedict XVI, in Ecclesia Unitatem, underscored the Successor of Peter's duty to safeguard unity as the visible principle of bishops and faithful, prioritizing common witness to encounter God. He invited prayer for unity through Mary's intercession. The Catechism reinforces that divisions hinder the Church's catholicity, stimulating efforts toward unity. Recent documents like The Bishop of Rome link synodality within the Church to ecumenical credibility, viewing her internal communion as a model for external relations.
The Church fosters unity through concrete actions: international commissions for theological dialogue with Eastern and Western Churches, yielding convergences on faith despite remaining challenges. These build on shared baptismal communion, enabling mutual enrichment and fuller koinonia. Local initiatives, catechesis, and diakonia integrate ecumenism organically into Church life. Cooperation in social fields—health, education, Bible translation—vividly expresses existing bonds and highlights Christ the Servant. Such efforts educate in unity, fostering desire to overcome disagreements.
The Church guards against false irenicism or indifferentism, praising true initiatives while correcting misinterpretations of Vatican II that offend faith unity. Renewal remains key: Catholics must aim at perfection, purifying the Church to delay no longer God's kingdom. In mixed marriages or diverse communities, ecumenism calls for prayerful conversion and fraternal service. The goal is organic communion in sacramental life and visible structure, under apostolic ministry led by Peter.
Despite progress—rebirth of unity awareness, dialogues producing results, and shared witness—the road is arduous. Differences in doctrine, especially on Christ, redemption, Church, and Mary, persist, alongside new movements causing confusion. Ecumenism demands no compromise on truth but overcoming divisions as a scandal weakening the Gospel. The Church learns to live this interim with trust, recognizing it as irreversible, impelled by the Spirit. Foundations like creeds and early councils unite, but doctrinal divergences require perseverance. In a unifying yet conflicted world, the Church must be a sign of reconciliation, interpreting signs of the times through ecumenism and mission.
The Catholic Church's role in fostering Christian unity is multifaceted: prophetic witness to Christ's undivided body, humble servant in dialogue and prayer, and beacon of renewal for full communion. By strengthening shared faith in the Trinity and creeds, developing koinonia's spirituality, and collaborating in charity—"in necessary things unity, in doubtful things liberty, in all things charity"—she advances toward the unity Christ wills. This journey, though challenging, fills with hope, as the Holy Spirit guides toward the one flock under one shepherd (Jn 10:16).