Amid the cacophony of the world, the human mind restlessly yearns for something whole, something nourishing. With so many competing voices speaking from our television sets, our radios, our computers or our phones, we wonder what in the world is true. How are we to find any sense of peace, much less any sense of God, with all this noise?

On 21 January 2022, Pope Francis declared St Irenaeus of Lyon to be a Doctor of the Church, a person whose teachings are sound, wholesome and life-giving for the people of God.

Specifically, Irenaeus has the title ‘Doctor Unitatis’: the ‘Doctor of Unity’. He is the Doctor of the Unity primarily in the sense that he provides a bridge between the Church in the East and the Church in the West. Born in Smyrna, modern-day Turkey, in the early half of the second century, he travelled West and ended up in Lyon, France, where he became the city’s second bishop. His thought reflects the best of both worlds, worlds that are often seen to be at odds with each other.

But there is a deeper sense in which Irenaeus is a ‘Doctor of Unity’. His most famous work is called Against Heresies, one of the earliest systematic expositions of the faith, and certainly the most sophisticated of his time.

To someone approaching Irenaeus for the first time, this work might seem intimidating. It deals with people and ideas far removed from our own, with problems seemingly irrelevant to the ones facing us today. But this need not be so. A running thread throughout Irenaeus’ arguments is an appeal to the absolute oneness of God; the God who is whole, unbroken and complete; the God who is the source of creation’s variety and multiplicity.

There are many dissonant aspects of creation: darkness and light, storm and quiet, the cruelty of nature and the compassion of its Maker. To explain this, people devised systems, and gods, that were the source of these incompatible experiences. But with only these systems to guide us, the world remains a cacophony; the ‘truth’ remains an endless, awful noise.

For Irenaeus, though, these seemingly irreconcilable aspects of creation were simply different notes in the Creator’s song. Two notes on a lyre played together might sound inharmonious, he says, but with the proper interval, they are not. The interval is what gives rise to the beauty of the ‘unbroken melody’.

The task of those who love the truth is to catch the music:

Those, too, who listen to the melody, ought to praise and extol the artist, to admire the tension of some notes, to attend to the softness of others, to catch the sound of others between both these extremes, and to consider the special character of others, so as to inquire at what each one aims (Against Heresies, II:XXV:2).

This music is reflected in the Church’s faith. Although the Church is ‘scattered throughout the world,’ the faith she has received is one she believes ‘as if she had but one soul, and one and the same heart, and she proclaims them and teaches them, and hands them down, with perfect harmony, as if she possessed only one mouth’ (I:X:2).

No matter where in the world the Church is planted, the faith is the same, which is part of the appeal. We long for wholeness.

This is why refuting heresies was so important for Irenaeus and others. The God who is whole and unbroken invites us to immerse ourselves in his own life; to become whole ourselves. A Church that sounds discordant, that plays notes that can’t be played together, isn’t able to reflect or search out the music of God.

When we think of unity, it’s easy to think of uniformity. Of a colourless whole that saps out uniqueness or individuality. But the unity Irenaeus wants us to consider is more like the unity of a song where all the notes, in their turn, contribute to the beauty of the whole. Obviously, a song can’t play any note it wants. Some don’t work. Some render the music offbeat, or take it in grating, horrible directions, away from the truth, away from God.

But to pray for unity is to pray that we might share the same music; that despite our clumsy fingers, God will teach us to play—and hear—the unbroken melody of his creation. When it feels like we are drowning in noise, the knowledge that there is such a melody should be a source of deep comfort for us.

The feast day of St Irenaeus of Lyon is celebrated by the Catholic Church on 28 June.