The Mystery We Confess
A Sermon for Trinity Sunday w/ Small Group Discussion Guide
Introduction
There are Sundays when the preacher’s task is relatively straightforward. Trinity Sunday is not one of those Sundays. Today, we are called to ponder the central mystery of the Christian faith: there is one God who exists eternally as Father, Son, and Holy Spirit. This mystery is to be confessed, not explained, so for those tempted to reach for clever analogies this morning to explain the Trinity, let me offer a gentle warning: heresy lies just around the corner from your favorite analogy.
So, to avoid falling into the very trap I have cautioned others about, my goal this morning is not to explain the mystery of the Trinity (as if we could fully comprehend it anyway). Instead, I aim to lead us into the biblical narrative and from there into confession and worship. This aim is entirely appropriate for Trinity Sunday because the doctrine of the Trinity did not arise from abstract theological speculation. The doctrine of the Trinity emerged from the lived experiences of the people of God.
The earliest Christians were adamant that there is only one God, the God of Abraham, Isaac, and Jacob. However, through their encounters with Jesus and their experience of the indwelling Holy Spirit, they realized that their monotheistic language needed to evolve. Without becoming polytheists, they acknowledged that there was more to God than simply his oneness. And so they explored new ways to articulate their belief in the one God they knew and worshiped as Father, Son, and Holy Spirit.1
St. Augustine once wrote, “If you have been able to comprehend it, it is not God.”
“If you have been able to comprehend it, it is not God.” - Augustine
The doctrine of the Trinity is not the Church’s attempt to comprehend God. Instead, with the doctrine of the Trinity, the Church endeavors to use our limited human language to define as clearly as possible who God has revealed himself to be. The doctrine of the Trinity is not a puzzle to be solved, nor a mystery to be unraveled; it is, rather, the Church’s best attempt at describing the one God we know as Father, Son, and Holy Spirit.
The Trinity in the Biblical Narrative
Thus, our discussion of the Trinity this morning begins not with abstract definitions or speculation but with the narrative of the Bible.
In creation, we encounter the Father who speaks, the Word by whom all things are made, and the Spirit who hovers over the face of the deep. In these opening verses of Scripture, God is already revealing himself as the eternal community of love and life.
In redemption, the story deepens. The Father sends the Son into the world, and the Son is conceived by the Holy Spirit. At Jesus’ baptism, the heavens open, the Spirit descends like a dove, and the Father’s voice speaks from above: “This is my beloved Son” (Matt 3:17).
As Jesus teaches and heals, he reveals the Father, promises the coming of the Spirit, and prays in communion with both. Before his death, he tells the disciples, “When the Spirit of truth comes, he will guide you into all the truth… He will glorify me, for he will take what is mine and declare it to you. All that the Father has is mine; therefore I said that he will take what is mine and declare it to you.” (John 16:13–15).
At Pentecost, the risen and ascended Christ sends the promised Holy Spirit upon the Church. The Spirit does not come as a vague force, but as the empowering presence of the Father and the Son, uniting us eternally to the Son, conforming us to his image, and bringing us into the divine life of God.
The Apostle Paul blesses the Church with these Trinitarian words: “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all” (2 Cor 13:14). And in Revelation 4–5, the heavenly worship expands from the creator God to the redeeming lamb, with the Holy Spirit hovering around the heavenly throne.
The Trinity, in other words, is not a doctrine that we impose on the Bible; it gives shape of the story itself. The Father creates, the Son redeems, and the Spirit sanctifies/ Yet, even this falls short of representing the glorious workings of the Trinity in the creation and salvation of the world.
What the Church Learned to Say
In time, the Church gave language to this mystery. The intention was not to tame it, but to guard it. The Trinity was not deduced by logic but confessed in doxology. It was formed in worship before it was ever formalized in writing. As the early Christians prayed, sang, baptized, read the Scriptures, and celebrated communion, they came to see that the God revealed in Jesus Christ and poured out in the Holy Spirit was not merely one God with multiple roles, but one being in three persons working together to create, redeem, and sanctify humankind.
To protect that confession, the Church gave us creeds. Among them, the Athanasian Creed stands out for its clarity and solemnity. This creed declares, “We worship one God in Trinity and Trinity in Unity, neither confusing the Persons nor dividing the Substance.” It insists that the Father is God, the Son is God, and the Holy Spirit is God, and yet there are not three Gods, but one God. Each person is co-eternal and co-equal, “So that in all things, as is aforesaid, the Unity in Trinity and the Trinity in Unity is to be worshipped.”
“We worship one God in Trinity and Trinity in Unity, neither confusing the Persons nor dividing the Substance.” - The Athansian Creed
The Athanasian creed concludes its first section with an uncompromising statement: “He therefore that will be saved must think thus of the Trinity.” These are weighty words, not because the Church seeks to gatekeep eternal life, but because it dares not proclaim any god other than the one God who has revealed himself in human history as Father, Son, and Holy Spirit. The creed is not a mathematical formula because if it were, it would fail. Instead, it is a doxological safeguard, drawn from Scripture and shaped by centuries of Christian experience and worship.
Cyril of Jerusalem wrote, “We do not explain what God is but confess what God has said: that he is Father, Son, and Holy Spirit.” The Athanasian Creed defends this mystery, not as a barrier to keep people out, but as a boundary to keep us from wandering outside the truth.
The Church does not and should not invent doctrine. Instead, it should bear witness to what God has revealed. And the doctrine of the Trinity, rightly confessed, keeps us centered on the one God who is Father, Son, and Holy Spirit from all eternity.
Why the Trinity Matters Now
We say of that one God that God is love. What many people who say those words forget is that love necessitates an object. C. S. Lewis writes in Mere Christianity, “All sorts of people are fond of repeating the Christian statement that ‘God is love.’ But they seem not to notice that the words ‘God is love’ have no real meaning unless God contains at least two Persons. Love is something that one person has for another person. If God was a single person, then before the world was made, He was not love.”
God is love because God is Trinity, or perhaps God is Trinity because God is love. God is not a solitary power, nor is he a distant abstraction. The God of the Bible is the God of eternal, life-giving, loving communion. The Father loves the Son. The Son loves the Father. The Spirit binds the Father and the Son together in perfect love. The doctrine of the Trinity is significant today because it reminds us that love is not secondary to God’s nature. It is not an addendum. Love is the deepest reality of what it means to be God.
The doctrine of the Trinity also reminds us that our salvation is not just eternal life, but also participation in the life of the Trinity. The Father sends the Son for us. The Son gives his life to redeem us. If salvation was merely that someone paid the price for our sins, then the story is over. But the story isn’t over. The Spirit is poured into our hearts so that we might share in the life of God. Paul says in Romans 8,
The Spirit himself bears witness with our spirit that we are children of God (Rom 8:16).
Likewise, as we saw last week, Paul writes in Galatians 4,
And because you are sons, God has sent the Spirit of his Son into our hearts, crying, “Abba! Father!” (Gal 4:6).
The Father has sent the Spirit of the Son into our hearts to bear witness to us that we too are children of God, children who can, with the eternally begotten Son, call him, “Abba” and “Father.” The Church Fathers taught that we become by grace what the Son is by nature. That is, we are drawn by the Holy Spirit into the life of the Son so that we may dwell forever in the love of the Father and the life of our Triune God.
Confession and Worship
So, what do we say this morning? We say that the Trinity is not a theory, but our best attempt to describe who God has revealed himself to be in human history and his Holy Word. Today we say that the Trinity is not an abstract philosophical or theological problem, but the living heart of our faith. Today we say that the Trinity is not a distraction from the Gospel, but the Gospel in its most profound truth.
As we recite the Creed today, don’t rush past its beauty and its drama. As we sing the Sanctus, let us remember that we are joining into the heavenly worship of the Triune God that has gone on since the world was made. As we come to the Table, let us give thanks to the Father, through the Son, in the power of the Holy Spirit.
To the Father who created us, to the Son who redeemed us, and to the Spirit who dwells within us and brings us into the divine life of our Triune God, to that one God be all glory, honor, and praise, now and forever.
Amen.
Small Group Discussion Guide
Introductory Prayer
Heavenly Father, as we gather to discuss the mystery of your triune nature, we ask that You would open our hearts and minds through Your Holy Spirit. Help us to move beyond trying to explain You, and instead lead us into a deeper worship and understanding of who You have revealed Yourself to be. In Jesus' name, Amen.
Ice Breaker
What's the most complex thing you've ever tried to explain to someone else? How did that experience go?
Key Verses
Romans 8:16
Galatians 4:6
1 Corinthians 8:6
Isaiah 6:1-3
Questions
Why does the sermon emphasize that the Trinity should be 'confessed, not explained'? What's the difference between these approaches?
How did the early Church's experience with Jesus and the Holy Spirit lead them to develop the doctrine of the Trinity?
The sermon mentions that 'God is love' has no meaning unless God contains at least two persons. How does the Trinity help us understand God's nature as love?
What were the two options available to early Christians regarding their understanding of God, and why did they choose a more complex path?
How does the sermon describe our salvation as more than just forgiveness of sins? What role does the Trinity play in this fuller understanding?
What does it mean when the sermon says we 'become by grace what the Son is by nature'?
How does the Trinity shape our understanding of worship and prayer?
In what ways does understanding the Trinity affect our daily Christian life and relationship with God?
Life Application
This week, when you pray, consciously direct your prayers to the Father, through the Son, in the power of the Holy Spirit. Notice how this Trinitarian approach affects your prayer life and understanding of God's work in your life.
Key Takeaways
The Trinity emerged from lived experience of God's people, not theoretical speculation.
God's nature as Trinity reveals that love is essential to who God is, not secondary.
Our salvation includes participation in the life of the triune God.
The Trinity is not a puzzle to solve but a mystery to confess and worship.
The doctrine of the Trinity safeguards essential truths about God's nature and work.
Ending Prayer
Triune God - Father, Son, and Holy Spirit - we thank You for revealing Yourself to us in love. Thank You for not remaining distant but drawing us into Your divine life through the work of Christ and the presence of Your Spirit. Help us to live in the joy of this relationship and to share Your love with others. In the name of the Father, Son, and Holy Spirit, Amen.
One of the more obvious examples of this the way Paul reworks the Shema (Deut 6:4) in 1 Cor 8:6.