Nicaea at 1700: The Problem With Unitate Fidei

Leo’s new apostolic letter wraps the Nicene Creed in synodality, then offers it as a participation trophy to “all Christian traditions”

Nicaea on the Jubilee Stage

Seventeen hundred years after the Council of Nicaea drew a hard line against heresy with anathemas and exile, Leo XIV has decided to mark the anniversary with an apostolic letter, In Unitate Fidei. The date is deliberate: Christ the King, 23 November 2025. The location is deliberate too: he is preparing a triumphant ecumenical pilgrimage to Türkiye, back to the place where the 318 Fathers met under Constantine and signed their names under homoousios.

On the surface the letter looks like the sort of thing a traditional Catholic could cheer. Leo praises the Creed, recites its phrases, retells the Arian crisis, and even rehabilitates the word “consubstantial” instead of hiding behind vague, modernist Christology. He quotes Athanasius. He speaks of divinization. He reminds us that only a truly divine Christ can defeat death and save us.

If all you read are paragraphs two through eight, you might almost forget which century you are in.

But this is not 325, and Leo is not Athanasius. The letter spends its first half sounding Catholic so that it can spend the second half sounding like the International Theological Commission: Nicaea as the foundation for a new, open-ended ecumenical process where “what unites us is greater than what divides us,” and where old doctrinal fights quietly lose their “reason to exist.”

The Council that once drove Arians out of the Church is now being asked to welcome everyone back without asking too many questions at the door.

From Creed to Ecumenical Brand

Once Leo puts the Catholic doctrinal scaffolding in place, the real agenda walks onto the stage.

Leo shifts from Nicaea’s battle with Arianism to the “ecumenical value” of the Creed today. He reminds us that the Nicene-Constantinopolitan Creed is professed in Orthodox liturgies and many Protestant services. He celebrates the fact that it became a “bond of unity between East and West” and later a common heritage of “all Christian traditions.” He calls it a model of “unity in legitimate diversity,” using the Trinity as the analogy: unity without diversity becomes tyranny, diversity without unity collapses into fragmentation.

In other words, the Creed becomes not simply the Catholic symbol of faith, guarded by Rome and received by her children, but a sort of shared logo for world Christianity. The emphasis subtly slides from the question “What is true?” to the question “What can we all say together?” The same text is now asked to bear incompatible systems: Catholic sacramental ecclesiology, Protestant invisible church theory, Orthodox rejection of universal papal jurisdiction. Everyone keeps their own commentary and calls it “diversity.”

Leo quotes John Paul II’s Ut Unum Sint and praises the “ecumenical movement” of the last sixty years. He assures us that we now recognize members of other churches and communities as brothers and sisters in Christ and that together we form one universal community of disciples. Full visible unity has not yet been reached; still, what unites us is greater than what divides us. That line appears again, as if repetition could make it less fragile.

The image is simple. Nicaea as the common campfire around which all baptized people can gather, each bringing their own theological accent, all warmed by the same flames.

The problem is that Nicaea did not gather everyone around a fire. It drew a sword.

“Controversies That Have Lost Their Reason to Exist”

The most revealing line in the entire letter is almost thrown away.

Leo says we must “leave behind theological controversies that have lost their raison d’être” in order to arrive at a common understanding and, even more, a common prayer to the Holy Ghost. He does not specify which controversies he has in mind. He simply assures us that some dogmatic battles no longer need to keep us apart.

This is where a Catholic formed by Pius XI and Pius XII hears the hinges creak.

Which controversies have lost their reason to exist? The Filioque clause, perhaps, mentioned in a footnote as a “subject of Orthodox-Catholic dialogue”? The scope of papal jurisdiction? Marian dogmas rejected by Protestants? The indissolubility of marriage? The doctrine of justification defined at Trent?

For centuries the Church insisted that unity required a common profession of all these truths. Pius XI wrote in Mortalium Animos that there is only one way to foster Christian unity: the return of separated brethren to the one true Church of Christ. Pius XII in Mystici Corporis taught that those divided in faith and government cannot be living in the unity of Christ’s Body. There is nothing tentative or provisional in their language. The doctrinal issues that divided Catholics and non-Catholics were not optional chapters to be revisited later; they were part of the deposit of faith.

Now Leo speaks of controversies that no longer justify division. He speaks of mutual conversion, as if the Catholic Church and those who reject her magisterium are all “on the way” toward a yet-to-be-defined future unity. He speaks of the Spirit leading us to discover a richer common faith together, without ever once saying that the path back to unity passes through submission to Roman primacy and acceptance of Catholic dogma.

Nicaea defined the Son as consubstantial with the Father and then anathematized anyone who said otherwise. Leo quotes the definition and buries the logic. The Creed is kept; the consequences are quietly retired.

Athanasius or the Spirit of Dialogue

Imagine explaining In Unitate Fidei to Athanasius.

You could tell him that Leo praises him by name, retells his heroic exiles, and calls his faith “unyielding and steadfast.” You could show him the passages where Leo insists that only a truly divine Christ can divinize man and defeat death. You could point to the beautiful prayer to the Holy Ghost at the end.

Then you would have to explain that, seventeen centuries later, bishops and theologians are still arguing whether the Holy Ghost proceeds from the Father alone or from the Father and the Son, and the Bishop of Rome calls this a “subject for dialogue.” You would have to explain that the primacy he fought to defend is now treated as an obstacle to unity that must be carefully reframed so as not to offend separated brethren. You would have to explain that Rome now prefers speaking of “legitimate diversity” rather than heresy, of “partial communion” rather than schism, of “common baptism” instead of conversion.

Athanasius was not exiled five times to preserve a lowest common denominator. He did not endure imperial pressure, slander, and violence so that future popes could place his Creed at the center of a process that treats serious doctrinal divisions as historical misunderstandings waiting to be transcended in prayerful dialogue.

The Church he knew believed that error kills souls and that charity demands clarity. Unity was measured by submission to the faith and to the visible head who protects it. Today’s ecumenical language measures unity by how often we appear together in photographs and how infrequently we mention what still divides us.

The apostolic letter praises the “Nicene youth” who finished the doctrinal work of the Creed. The tone of the document itself belongs to the synodal adult who has learned not to say anything too sharp in mixed company.

What This Really Tells Us About Rome

So what should a serious Catholic take from In Unitate Fidei?

The same Rome that quotes the Creed now uses it as an ecumenical brand. The very symbol composed to draw a line between truth and error is recast as a capacious umbrella that can shelter mutually exclusive systems as long as they all recite the same words. The Council that once condemned and expelled is now invoked to justify a unity that is content to remain incomplete, a communion that never quite requires anyone to change their mind.

Third, the pattern. When Leo speaks about the Church, he sounds like Vatican II. The Creed is stable; ecclesiology is up for revision. The old teaching on who belongs to the Church and how separated brethren must return is politely replaced by a language of mutual enrichment and shared heritage. The theological controversies that once justified a Reformation and a millennium of schism are suddenly candidates for retirement..

If there is any lesson to draw on this anniversary, it is that unity without truth is counterfeit. The 318 Fathers did not sit in council to discover the minimum content necessary to stay in communion with Arius. They defined the faith and suffered the consequences. If Leo wishes to celebrate their courage, he will have to recover their clarity.

Until then, the Nicene Creed will continue to stand in judgment over the very ecumenical project being built on its shoulders. The words remain the same. The question is whether Rome still believes everything they imply.

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