Pope Leo: Repent sins, bear witness, foster Christian unity

By Dr. Jeff Mirus ( bio - articles - email ) | Nov 25, 2025

In the new Apostolic Letter In Unitate Fidei it is a pleasure to see Pope Leo doubling down on the importance of Christian unity precisely by not watering down the Catholic Faith, but rather by insisting on the absolute truth of the fundamental Catholic creed set forth by the Council of Nicaea in 325 AD. One of the primary purposes of that Creed was to deny the Arian view that Christ was not eternal like the Father, but somehow “made” by the Father at some point before the creation of the world. Attributed to a Christian presbyter named Arius, this understanding was one of a great many distortions of the person of Christ which arose in the first centuries of Christianity, and which the Church found it necessary to correct.

Sadly, of course, other sorts of distortions have continued to arise throughout history, leading groups of Christians to break with the Church founded by Jesus Christ in favor of their own interpretations of Divine Revelation. Clearly we are plagued by the same problem today, but disagreements over the nature(s) and personhood of Jesus Christ were, perhaps for obvious reasons, among the most heated controversies in the first few centuries of the Christian era. Thus, Pope Leo has taken advantage of the 1700th anniversary of the great Council of Nicaea, which definitively corrected the mistaken assumption that Christ was not “true God from true God” but rather a lesser being who served as the intermediary between us and our inaccessible Father.

Today too Christ means different things to different people. But among other valuable lessons learned from the Council of Nicaea is that the Christian faith cannot be preserved in its fullness without a Divinely-guaranteed teaching authority. Anyone who knows anything about the history of Christianity should have noticed how often it has been necessary for the Church to examine controversies, reject falsehoods, and define the fundamental truths of the Faith more precisely as new errors in understanding arise over time. Our current pope recognizes how disastrous these errors—and their resulting divisions—have been over the years, and so he has chosen to emphasize the profession of Faith at the Council of Nicaea both as a reminder of the need for Christian unity based on the Church’s creedal affirmations and as a corresponding warning against the sort of private judgment which has distorted Revelation and led to a tremendous weakening of Christian witness down through the centuries.

Baptismal Commitment

Pope Leo points out that as Christianity spread so did confusion about Catholic teachings as they were contested by the patterns of thought characteristic of other cultures, especially those of the Greeks and Romans. This led to the development of creedal affirmations which emphasized essential points of Faith, often used also in the baptism of adults. Reflecting on the creedal formulation at the Council of Nicaea, the Pope notes:

In order to express the truth of the faith, the Council adopted two words—“substance” (ousia) and “consubstantial” (homooúsios)—which are not found in Scripture. The Council’s intention in doing so was not to replace biblical statements with Greek philosophy. On the contrary, the Council used these terms precisely to affirm biblical faith with clarity and to distinguish it from Arius’ error, which was deeply influenced by Hellenism. [#5]

The Pope goes on to discuss the work of St. Athanasius and the Christian growth in understanding of what it means for the human person to be “divinized” (also a theme in the writings of St. Paul). Leo points out that “divinization in no way implies the self-deification of man. On the contrary, divinization protects us from the primordial temptation to want to be like God (cf. Gen 3:5). What Christ is by nature, we become by grace” [#7]. Divinization, the Pope writes, “is true humanization (becoming fully human). This is why human existence points beyond itself, seeks beyond itself, desires beyond itself, and is restless until it rests in God.” Or again, “Only God, in his infinity, can satisfy the infinite desire of the human heart, and for this reason the Son of God chose to become our brother and redeemer.”

A Long Way to Go

This Apostolic Letter offers a double challenge. First, we must recognize that a great many people at the time of Nicaea and in its aftermath had to vigorously combat error in order to restore and preserve the unity of the Faith. Second, we must see that the same holds true for us. Leo emphasizes that “the Nicene Creed invites us to examine our conscience”. Citing the Second Vatican Council to the effect that Christians are at least partly responsible for the fact that “for many people today, God and the question of God have almost no meaning in their lives”, the Pope points out that too often Catholics do not bear witness to the faith: “They hide the true face of God with lifestyles and actions that diverge from the Gospel” [#10].

If we are honest, we know this is true, and we know that most of us bear some part of the blame. Thus Leo challenges all of us to examine our consciences and to get rid of our idols: “Naturally,” he writes, “following Jesus Christ is not a wide and comfortable path. However, this often demanding or even painful path always leads to life and salvation” [#11]. The Pope also points out that “in order to carry out this ministry credibly, we must walk together to reach unity and reconciliation among all Christians” [#12]. One of the main purposes of this Apostolic Letter is to propose that the “Nicene Creed can be an important reference point for this journey. It offers us a model of true unity in legitimate diversity. Unity in the Trinity, Trinity in Unity, because unity without multiplicity is tyranny, multiplicity without unity is fragmentation”.

“The restoration of unity among Christians does not make us poorer,” concludes Pope Leo. “On the contrary, it enriches us.” And so the Apostolic Letter closes by inviting all of us to begin our recommitment to both Christian witness and Christian unity by invoking the Holy Spirit through the following prayer:

Holy Spirit of God, you guide believers along the path of history.

We thank you for inspiring the Symbols of Faith and for stirring in our hearts the joy of professing our salvation in Jesus Christ, the Son of God, consubstantial with the Father. Without him, we can do nothing.

Eternal Spirit of God, rejuvenate the faith of the Church from age to age. Help us to deepen it and to return always to the essentials in order to proclaim it.

So that our witness in the world may not be futile, come, Holy Spirit, with your fire of grace, to revive our faith, to enkindle us with hope, to inflame us with charity.

Come, divine Comforter, source of harmony, unite the hearts and minds of believers. Come and grant us to taste the beauty of communion.

Come, Love of the Father and the Son, gather us into the one flock of Christ.

Show us the ways to follow, so that with your wisdom, we become once again what we are in Christ: one, so that the world may believe. Amen.