Pope Leo XIV invokes Leo XIII as early champion of ecumenism

VATICAN CITY (LifeSiteNews) — Pope Leo XIV marked the start of the Week of Prayer for Christian Unity by invoking the legacy of Pope Leo XIII, whom he presented as an ecumenical forerunner.

On January 18, at the conclusion of the Angelus prayer in St. Peter’s Square at the Vatican, Pope Leo XIV announced the opening of the Week of Prayer for Christian Unity, encouraged Catholics to pray for full visible unity among Christians, and referred to Pope Leo XIII as a historical precursor who had promoted prayer for Christian unity.

“Today begins the Week of Prayer for the Unity of Christians,” Leo XIV declared, adding that “the origins of this initiative go back two centuries, and Pope Leo XIII encouraged it greatly,” before inviting Catholic communities to intensify prayer “for the full visible unity of all Christians.”

The Week of Prayer for Christian Unity begins annually on January 18. The theme for this year is taken from Ephesians 4:4: “One body and one Spirit, as one is the hope to which you were called.” The accompanying prayers and reflections prepared for the week have been coordinated by an ecumenical group under the Department for Interreligious Relations of the Armenian Apostolic Church.

The Pope’s reference to Leo XIII places the late 19^th century pontiff within the historical narrative of prayer initiatives for Christian unity. Leo XIII, who reigned from 1878 to 1903, repeatedly encouraged prayers for unity and addressed the question of divisions among Christians in several major magisterial documents.

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However, the intentions expressed by Leo XIII in his official teaching differed in emphasis from contemporary ecumenical approaches. In the encyclical Satis Cognitum about the unity of the Church, promulgated on June 29, 1896, Leo XIII taught that such unity is visible, grounded in shared faith, the sacraments, and governance. The document explicitly rejected the idea of an invisible or merely spiritual Church and affirmed that full unity requires adherence to the authority established by Christ.

In Satis Cognitum, Leo XIII wrote also that those who accept only parts of Christian doctrine according to personal preference “do not rely on faith, but on their own judgment,” insisting that authentic unity cannot be separated from the integrity of revealed doctrine. The encyclical presented the unity of the Church as inseparable from obedience to Christ and from communion with the See of Peter.

A similar missionary orientation appears in the apostolic letter Caritatis Studium, issued on July 25, 1898. In that document, Leo XIII addressed Anglicans directly, inviting them to reconciliation with Rome. He urged them to recognize the primacy of Peter and to acknowledge what he described as the orthodoxy of Catholic doctrine, while rejecting Protestant theological positions that had emerged after the Reformation. The letter framed unity as a return of separated Christians to full communion with the Catholic Church.

He wrote that his “ardent charity” for Christians outside Catholic communion compelled him “to bring back to the embrace of the Good Shepherd those whom manifold error causes to stand aloof from the one Fold of Christ,” explicitly describing separation as the result of doctrinal error.

Leo XIII further stated that he was “constantly imploring” Christians separated from the Church “to agree at last to restore together with Us the communion of the one and the same faith,” presenting unity as the recovery of a shared faith in communion with Rome. This understanding was inseparable from Leo XIII’s teaching on ecclesial authority, since, as he affirmed, “the supreme teaching authority was committed to one, on whom, as on its foundation, the Church must rest,” referring to the primacy given by Christ to St. Peter.

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By contrast, Pope Leo XIV’s recent magisterial teaching situates unity within a contemporary ecumenical framework. In the apostolic letter In Unitate Fidei, issued in November 23, 2025, Leo XIV addressed the pursuit of Christian unity in the context of dialogue between Churches and ecclesial communities.

Pope Leo XIV presents an understanding of Christian unity that differs in approach from that articulated by Leo XIII at the end of the nineteenth century. While grounding ecumenical efforts in the shared profession of the Nicene-Constantinopolitan Creed, Leo XIV states that contemporary unity “does not imply an ecumenism that attempts to return to the state prior to the divisions,” explicitly distancing present initiatives from a model of reunion based on return. Instead, he describes an ecumenism that “looks to the future” and “seeks reconciliation through dialogue as we share our gifts and spiritual heritage.”

Within this framework, the Nicene Creed is proposed as “the basis and reference point” for the journey toward unity, offering “a model of true unity in legitimate diversity.” The Pope further calls on Christians to “leave behind theological controversies that have lost their raison d’être”, presumably like the Filioque controversy, in order to develop “a common understanding and even more, a common prayer to the Holy Spirit.”

Finally, Leo XIV notes that ecumenical dialogue has already led Christians “to recognize the members of other Churches and ecclesial communities as our brothers and sisters in Jesus Christ,” affirming that, despite the absence of full visible unity, “what unites us is much greater than what divides us.”