Pope Leo XIV Issues In Unitate Fidei to Mark 1,700 Years Since the Council of Nicaea

Calls for renewed Christian unity rooted in the Nicene Creed

Photo: Vatican Media

Vatican City, 23 November 2025 — Pope Leo XIV has released a new Apostolic Letter titled In Unitate Fidei (“In the Unity of Faith”), commemorating the 1,700th anniversary of the First Council of Nicaea. The letter, published on the eve of the Holy Father’s Apostolic Journey to Türkiye, invites Christians worldwide to return to the foundational faith expressed in the Nicene Creed and to strengthen efforts toward full Christian unity.

The Pope described the anniversary as a “moment of grace,” emphasizing that the gift of faith handed down from the early Church must be “guarded, lived, and transmitted with renewed conviction.” The Council of Nicaea, convened in A.D. 325, gave the universal Church its first solemn profession of faith and defined the full divinity of Jesus Christ, decisively rejecting Arianism.

A Call to Rediscover the Creed

In his letter, Pope Leo XIV insists that the Nicene Creed is not merely a historical document but a “living confession” that continues to shape Christian identity and mission. He includes the text of the Creed in full, noting that its proclamation binds all Christians who profess belief in “one Lord Jesus Christ, true God from true God.”

Echoing the challenges faced by the early Church, the Pope highlights the importance of affirming Christ’s true divinity in today’s world. “Only the Son who is consubstantial with the Father,” he writes, “is able to save, redeem, and divinize humanity.”

An Appeal for Ecumenical Progress

A substantial portion of In Unitate Fidei is dedicated to ecumenism—one of the defining themes of Pope Leo XIV’s pontificate. The Holy Father urges Christians of all traditions to journey together “in patient dialogue, mutual listening, and sincere conversion of heart.” The aim, he clarifies, is not to erase legitimate differences but to base unity on the shared faith articulated at Nicaea.

The Pope calls for an intensified “common prayer to the Holy Spirit,” whom he describes as the divine bond of unity within the Trinity and among believers. True Christian reconciliation, he says, must be rooted in the Spirit’s work.

Faith as a Guide for Social and Moral Renewal

Beyond theology, the letter draws strong connections between belief and action. Pope Leo XIV reminds the faithful that the Creed must inspire a renewed commitment to justice, care for creation, and compassion for the poor. Authentic worship of God, he states, is inseparable from concrete service to one’s neighbor.

“The mystery we profess in the Creed,” he writes, “must shape our way of living, our stewardship of creation, and our solidarity with the most vulnerable.”

A Prayer for the Church

The Apostolic Letter concludes with a solemn invocation to the Holy Spirit, asking for the renewal of faith, the strengthening of hope, and the rekindling of charity. It is a plea for unity—within the Catholic Church and across the entire Christian world.

A Milestone Moment for Global Christianity

As preparations continue for Pope Leo XIV’s trip to Turkey, including a planned visit to the historic site of ancient Nicaea, In Unitate Fidei sets a reflective and forward-looking tone. The letter situates the 1,700-year legacy of the Council of Nicaea within today’s global challenges, calling all Christians to reaffirm the foundational truths of their faith and to work tirelessly for unity.