What is God? When the biblical Jews asked that question, they responded from their experience of salvation history. God is the one who told me to leave behind everything I knew and set out for God-knows-where, says Abraham. God is the one who asked me to go back to the land of oppression and enslavement so I could speak truth to power, says Moses. God is the one who made a covenant with us on Mount Sinai, in the cloud of unknowing. God is the one who remembered us in the days of exile. God is the one who brought us home from Babylon.
Then Jesus came along, and even though he lived and died as a human being, there were those who experienced the fullness of God in the unique particularity of his life, death, and resurrection. The risen Lord, who said “I am with you always,” would become an object of worship very early in the life of the Church.
And after the Ascension of Jesus came the Holy Spirit, not only as an indwelling presence but also as a radically transformative force, in whom divine fullness was equally and uniquely manifest.
For the early Christians, then, the One they called God had been revealed to have three distinct ways of being: Source, Savior, and Spirit. Love who loves us; Word who saves us; Spirit who renews us. And before long they were offering worship not only to the God of Israel, but to Jesus and the Holy Spirit as well.
They were not polytheists. They rejected pagan notions of a heaven and earth populated by competing deities. But their experiences of God in Christ and God in the Spirit were unique enough to differentiate them from the Holy One who sent Jesus into the world.
At the same time, the second and third Persons were not understood to be partial or lesser versions of God. Only the true God can save us, as Christ did. Only the true God can sanctify us, as the Spirit does.
Those first Christians couldn’t deny their experience, or the witness of Scripture. Christ was God. The Spirit was God. But that posed a conceptual problem.
How can the Three be One? How can the One be Three? Mathematics or logic can’t solve this puzzle. Several centuries of ecumenical councils struggled with the questions, doing their best to preserve the paradox of Three in One and One in Three from collapsing into the simplicity of God as “One is One and all alone.”
Although it would have put a lot of theologians out of work, It would have been a lot easier just to stick with the Oneness. But that would not have been true to Christian experience. The Threeness is essential to our informed—and formative—encounters with God. As contemporary Catholic theologian Catherine LaCugna puts it, “The doctrine of the Trinity is ultimately a practical doctrine with radical consequences for Christian life.” 
Does that mean that the friends of God have to master the bewildering terminology and complicated nuances of ancient dogma in order to live the Christian life? Will heaven admit only the most sophisticated thinkers? Let’s hope not.
I’ve read a lot of theology and Church history over the last fifty years, and I still have trouble remembering the differences between Monophysites, Monothelites, Monarchians, Modalists, Ebionites and Sabellians. As Japanese theologian Kosuke Koyama wonders, what if we were to exchange the metaphysical tangles of the West for more down-to-earth analogies. For example, he asks, what might the yin-yang of “pepper” and “salt” tell us about the divine nature?  Or St. Patrick’s shamrock, for that matter.
For the Offertory anthem at the liturgy for Trinity Sunday, Mozart’s Laudate Dominum, I’ve assembled 26 concrete images of persons and objects grouped in threes. As you watch the video, I invite you to contemplate the Christian koan of Three-in-One and One-in-Three.
Now then, what shall we say about the Trinity? One of the sixteenth-century reformers counseled intellectual modesty. “We adore the mysteries of the Godhead,” he said. “That is better than to investigate them.”  In a similar vein, a contemporary theologian reminds us that the “triune God is not simply unknown, but positively known to be unknown and unknowable—which is a dear and profound knowledge.” 
But on Trinity Sunday, it is the preacher’s ritual duty to offer a sacrifice of ignorance on the altar of unknowing. So here we go.
Back in the day—the fourth century, that is—when the Council of Nicaea was parsing theories of the divine life, theology was a popular sport, and people kicked around trinitarian doctrines the way some of us recite the arcane numbers of baseball metrics today. But in the late Middle Ages, the doctrine of the Holy Trinity went into cold storage. By the time of the Enlightenment, Immanuel Kant could say that Trinitarian theology had “no practical relevance at all, even if we think we understand it.” 
In recent centuries, any sort of God talk has been drained of content for many people. We live in a secular age, where a divine power who is in but not of the world has become increasingly unthinkable. Religion, in the world’s eyes, has become more of a private matter than a public truth.
And yet, the Spirit continues to work, and in the last few decades we have seen a remarkable resurgence of attention and thought devoted to the meaning and relevance of the Trinity. It’s not just white, western males doing this work. Feminists, Africans, Asians, Middle Easterners and Latin Americans are all bringing fresh and urgent perspectives to Christianity’s core doctrine of God. And their work is of enormous consequence for both our personal faith and our common life.
The Nicene Creed declares that the three Persons are “of one substance.” In other words, whatever God is made of, Father, Son, and Holy Spirit have all got it—and in equal measure.
But what is that “substance?” Is it a divine essence which existed prior to, or in addition to, the Persons themselves? Is there a one God hidden behind or beyond the Trinity? Such a notion would undercut the completeness of the Trinity, making it dependent on something external—in other words, less than fully divine in itself.
Or is the divine substance like a pie which has been cut into three equal pieces? That would divide God into parts and lose the unity of the whole. It would also make the Persons less than eternal, since the whole pie would have to precede the creation of the separate pieces.
But what if we were to give up the idea of divine “substance” as some kind of stuff which exists on its own and gets divided into three, or possesses a reality in addition to whatever the three Persons consist of? What if being the divine Trinity does not mean to have a divine substance, a kind of primordial stuff. What if being a Trinity means to be in relation with one another?
Perhaps the Trinitarian God is best described not as a fixed, objective entity, but as an event or activity, an eternal communion shared between the Persons. The Greek word perichoresisdescribes the divine communion as a dance where the partners are in continuous motion, weaving in and out of one another.
This conceptual shift from substance to relation is a central theme of contemporary theology. As feminist theologian Elizabeth Johnson writes (using inclusive terms for the Persons):
“The mutual coinherence, the dancing around together of Spirit, Wisdom and Mother; or of mutual Love, Love from Love, and unoriginate Love; or of the three divine persons – this defines who God is as God. There is no divine nature as a fourth thing that grounds divine unity in difference apart from relationality. Rather, being in communion constitutes God’s very essence.” 
A couple of British theologians elaborate this point when they say that the divine Persons do not “exist over against the others as self-enclosed centers of consciousness, as with human persons … but rather each dwells in the other through a kind of inter-permeation.” Then they sum it up this way: “The consciousnesses are fused but not confused.” 
This is not a new idea. The First Epistle of John assures us that “God is love” (4:8). And love, as we all know, cannot exist alone, without an “other” to share with, give to, receive from. Love exists only by going beyond the self in a process of perpetual self-offering.
Love is not a secondary or optional property of God. Love is who God is, and how God exists. Simply put: “the Trinity is not derived from God’s essence; the Trinity is God’s essence.” The communion and community of the Persons is God’s nature and essence.” 
Jürgen Moltmann notes the impossibility of a loving God being otherwise. “God cannot find bliss in eternal self-love,” he writes, “if selflessness is part of love’s very nature. God is in all eternity self-communicating love.”  A Kenyan Christian, John Mbiti, who comes from a more communal culture, puts this even more succinctly:
“I am because we are, and since we are, therefore I am.”
We may struggle with this interdependent Trinitarian model because our culture has taught us to think of a person as an autonomous individual, whose identity, mind and will are separate and independent from every other person.
But what the doctrine of the Trinity tells us is that you cannot be a person alone. You can only be a person in relationship with others. Addressing another, listening to another, conversing with another, loving one another, offering ourselves to one another—these are the means of becoming a person and existing as a person, if we are to live in the image of the relational personhood of the divine, in whom the one does not exist without the many.
When we hear Jesus say, you must lose yourself to find yourself, we may think he’s speaking of death, either metaphorical or physical, some kind of painful stripping away. And sometimes that is the case.
But I think Jesus is also describing the divinely grounded process of communion and community. “I am because we are, and since we are, therefore I am.” St. Athanasius had a wonderful term for this state of being in communion. He called it “reciprocal delight.” We are all in this together, God says, and so say God’s friends as well.
It seems especially fitting at this particular moment to contemplate communion as the essential and constitutive fact of divine life, for in one week’s time we will gather together, in person at last, as the Body of Christ at St. Barnabas. It has been fourteen months since we last did this. What joy it will be to share the sacrament of God’s self-diffusive love once again and celebrate the bonds between us.
After so many words about the Holy Trinity, let me conclude with an image. Thirty years ago, Polish film director Krzysztof Kieslowski made a series of 10 one-hour films called Decalogue. Each of the films is based on one of the Ten Commandments, and the series is one of the masterpieces of spiritual cinema. 
In the first film, there’s an exchange between Pawel, an eleven-year-old boy, and his aunt Irena. Pawel has a great curiosity about God, which his single-parent father, an unbeliever, cannot satisfy. So Pawel takes his questions to Irena, his devout Catholic aunt:
Pawel: Do you believe that God exists?
Pawel: What is God?
Irena doesn’t answer with words.
Instead, she puts her arms around Pawel and pulls him close.
Irena: What do you feel now?
Pawel: I love you.
Irena: Exactly. That’s what God is.
 Catherine M. LaCugna, cited in Veli-Matti Kärkkäinen, The Trinity: Global Perspectives (Louisville, KY: Westminster ]ohn Knox Press, 2007), 179.. This is the opening sentence of LaCugna’s God for Us: The Trinity and Christian Life (1991). As you will see, I found Kärkkäinen’s study of recent Trinitarian theology to be an invaluable resource.
 Veli-Matti Kärkkäinen, 312.
 Philip Melanchthon, in Veli-Matti Kärkkäinen, xvi.
 Elizabeth Johnson, in Veli-Matti Kärkkäinen, 212, from Johnson’s She Who Is: The Mystery of God in Feminist Theological Discourse(1993).
 Immanuel Kant, in Veli-Matti Kärkkäinen, 206.
 Elizabeth Johnson, in Veli-Matti Kärkkäinen, 56.
 Ninian Smart & Steven Konstantine, in Veli-Matti Kärkkäinen, 249, from their Christian Systematic Theology: Theology in a World Context (1991).
 Richard Rice, in Veli-Matti Kärkkäinen, 140.
 Jurgen Moltmann, in Veli-Matti Kärkkäinen,106; from Moltmann’s classic Trinity and the Kingdom: The Doctrine of God (1981)
 John Mbiti, in Veli-Matti Kärkkäinen, 352.
 Matthew 10:38.
 St. Athanasius (c. 296-373), a bishop in Roman Egypt, was a key defender of Trinitarianism. Cited in in Veli-Matti Kärkkäinen, 39.
 See my post, Kieslowski’s Decalogue: A Masterpiece of Religious Cinema (Jan. 28, 2017): https://jimfriedrich.com/2017/01/28/kieslowskis-decalogue-a-masterpiece-of-religious-cinema/