The new Apostolic Letter In unitate fidei by Pope Leo XIV arrives at a historical moment in which religious confusion is no less insidious than the turmoil that shook the Church in the fourth century. Then as now, faith risks being reduced to a symbolic language, a private emotion, a moral portrait of Jesus rather than the concrete confession of God made man. The Pope brings the entire Church back to the source: the Nicene profession of faith, the heart of Christianity, “because in Jesus Christ, consubstantial with the Father, God has become our neighbor.”
Leo XIV’s work is not archaeology; it is a judgment on the present. To understand it, one must grasp the theological logic the Letter employs—a logic that shines precisely where early Christian thought reached its maturity. And its core threads emerge from what the great patristic tradition always taught: faith cannot endure unless it preserves the full mystery of Christ
The decisive question is not “What do we think about Jesus?” but “Who is Jesus?”
The Apostolic Letter recalls that the question asked at Caesarea Philippi - “Who do you say that I am?” - is not an ancient echo but the living crossroads that always separates authentic faith from its caricature. Leo XIV shows that Arianism was not an accidental episode in history but a recurring temptation: reducing Christ to an intermediary, an exalted being yet not fully God. The same logic that once threatened the faith - the greatest danger to Christian doctrine because it denied the Son’s real participation in the Father’s essence - reappears today in subtler forms: Jesus as a moral teacher, a spiritual symbol, an “energy of goodness.”
This is why the Letter restates with clarity the Nicene formula: “begotten, not made, of one substance with the Father”. This is not technical theology; it is the very condition for saying anything true about salvation. Faith cannot rest on vague religious feelings. Faith “stands or falls” on the Son’s consubstantiality.
Without the true divinity of the Son, salvation does not exist.
In unitate fidei forcefully recalls what the ancient tradition understood with radical clarity: only God saves. If Christ is not fully God, redemption dissolves into myth. Leo XIV states this openly by drawing from the patristic core: salvation is not an idea, nor psychological comfort, nor an ethical journey; it is the incursion of the Infinite into human flesh. Christ “descended” for us – descendit - a word the Pope highlights because it contains the whole Christian paradox: the downward movement of the Most High, the self-emptying that reveals glory. The Letter shows that the truth of the Incarnation - total, real, without docetic reductions - is what ensures that our humanity has been reached in all its depths, redeemed in both body and soul, in what is most fragile and most great within us.
Early Christian theology insisted on one principle: God truly became man to make man capable of God. Without this ontological reality, Christianity becomes moral philosophy. With it, Christianity becomes an event: our nature is raised, healed, divinized.
The real problem of ancient Arianism - and its modern versions
Leo XIV’s reading is not nostalgic; it is surgical. The Pope sees that the contemporary crisis - Christological relativism, psychological reduction of faith, doctrinal uncertainty - arises from the very root the Fathers fought: a concept of God that is too small. For Arius, the Son was an intermediate being, unable to know the Father fully, subject to change. Leo XIV shows that similar notions circulate today beneath more refined language: “Christianity as inspiration,” “Jesus as an exceptional prophet,” “God as pure spiritual energy.” The Apostolic Letter responds by affirming that the infinite distance between God and humanity has been bridged only because the Son is God. And it adds a crucial point: the Incarnation is not a sacred myth but a historical, concrete, verifiable fact, held by the faith with the firmness of the Creed.
Unity of faith is not uniformity, but communion in truth
In unitate fidei does not propose doctrinal rigidity. It proposes a criterion: Christian unity arises only if the truth of Christ is preserved integrally. Like the Fathers of Nicaea - guided by the conviction that the Church transmits a received faith, not an invented one - Leo XIV asks the Church today not to bend doctrine to cultural fashions. The Pope is not speaking of nostalgia but of foundations: the Creed is not the past; it is the compass for navigating times of bewilderment. Christianity without dogma dissolves into spiritualism. Christianity with dogma lives because it remains anchored to the event from which it was born.
Nicaea as light for the present: a Christianity capable of inhabiting history
Leo emphasizes a point the ancient theology showed with force: God is not a static and distant being, but the One who enters history, even into its wounds. This dismantles the caricature of an “immutable” God as indifferent. True divine immutability - as the Fathers taught - is the immutability of self-giving love, not inertia. This is why the Pope connects the profession of faith with the wounds of the world: wars, injustices, fears. Not because the Gospel is a social tool, but because only God-with-us can be a credible hope for humanity.
Hope is not an idea. It is a Presence
What In unitate fidei tells us is clear: the Church cannot lose Christ without losing herself. This magisterial text is an act of guardianship and freedom. Guardianship of the apostolic faith; freedom from cultural trends that wish to reduce Christianity to just another discourse. Leo XIV places again at the center what the Fathers defended with courage and intelligence: only if Christ is true God and true man is Christianity truly good news. Everything else - reductionist, symbolic, spiritualistic interpretations - is nothing but an elegant revival of an ancient temptation: a God who does not save, a Christ who does not change life, a faith that does not generate hope.
Marco Felipe Perfetti
Silere non possum