As the Church prepares for Pope Leo XIV’s upcoming trip to Türkiye, the Holy Father has released a new Apostolic Letter, In unitate fidei, to mark the 1700th anniversary of the First Council of Nicaea. Published on the Solemnity of Christ the King, the document offers the faithful a fresh invitation to renew their love for the ancient profession of faith that has shaped Christian life from the earliest centuries.
The anniversary commemorates the pivotal gathering of bishops in 325 AD, when the Church articulated its teaching on the divinity of Christ and expressed that truth in what would become the Nicene Creed. Pope Leo’s visit will bring him to Ankara, Istanbul, and İznik, the historic site of the council itself. In this context, the new Letter calls the Church to reflect with gratitude on the unity secured at Nicaea and the hope that still flows from its teachings.
At the heart of the Letter is an appeal for Christians to walk together with renewed confidence in the faith first handed on by the apostles. The Pope points to the Creed as a treasure that has been safeguarded for centuries, a proclamation that continues to nourish believers each Sunday as the Church professes the mystery of the Son of God who became man for our salvation. This shared confession, he writes, remains an anchor in times marked by turmoil, war, inequality, and widespread suffering. In a world beset by fear and instability, the enduring profession of faith continues to strengthen the Church with hope.
Pope Leo also stresses the profound ecumenical significance of Nicaea. The Council’s teaching unites Christians across traditions, and the Pope notes that decades of dialogue have helped believers recognize one another as brothers and sisters in Christ. Although full visible unity has not yet been achieved, the bond formed through baptism and the shared proclamation of the Creed continues to draw Christians closer. The Pope observes that the common witness of martyrs across the centuries remains a powerful sign of unity, urging all the faithful to pursue reconciliation and peace.
The Letter emphasizes that genuine ecumenism looks forward rather than backward. The Holy Father encourages Christians to set aside disputes that belong to another era and instead cultivate a deeper mutual understanding. This journey, he explains, does not demand a return to earlier forms of unity nor an acceptance of present divisions. Rather, it requires patient dialogue, shared prayer, and an openness to the gifts present in each Christian community. Such an approach does not diminish the Church, he writes, but enriches it by drawing believers into a fuller communion rooted in truth and charity.
Pope Leo concludes by presenting the Nicene Creed as a guide for this ongoing work. The Creed stands as a steady point of reference, offering clarity and direction as Christians seek unity. He invites all the faithful to entrust this mission to the Holy Spirit, whose light gathers the Church into one body and strengthens her witness before the world.
Through In unitate fidei, the Holy Father calls the global Church to embrace the grace of this anniversary year with renewed devotion. The faith proclaimed at Nicaea remains the foundation upon which Christians build their hope, and Pope Leo now urges the Church to allow that same faith to guide her toward deeper unity and a more compelling testimony to Christ.
Read In unitate fidei here.