Gregory of Nyssa once wrote, “The chief point of Christian piety is to believe the only begotten God” (John 1:18). His contemporary and friend Gregory of Nazanzius similarily said, “The Trinity is the chief topic of Christianity.”
I suppose if someone asked us what the chief topic of Christianity is, then we would reply, “Jesus” or “the Gospel.” But our answer and the earlier answers do not disagree with each other. In truth, they speak about the same reality but from different viewpoints. To confess the Trinity is to confess the Gospel of Jesus Christ, the only begotten of God.
What Is the Gospel?
The Gospel is good news about what God has done in Jesus the Messiah. Paul sums up the Gospel through affirming the death, burial, resurrection, and appearance of Christ according to the Scriptures (1 Cor 15:3–5).
The repeated phrase “according to Scripture” forms a key to understanding the Gospel. That is, the work of Christ accords with the Old Testament revelation. Hence, we have a massive interpretive matrix through which to understand the revelation of Jesus. We know that God created, promised, and sent prophets to Israel. We know that the creator God who chose Israel promised to send a Saviour, to visit his people.
Hence, God’s promise to visit and to heal his people came to fruition when Jesus, the life-giving Spirit (1 Cor 15:45), came to earth. Put more theologically, the Father sent the Son to fulfill his promise. But during his sojourn and post-resurrection appearance, Jesus relayed to his disciples that his work would come to completion through the Holy Spirit.
Before ascending to heaven, Jesus breathed on the disciples and said, “Receive the Holy Spirit” (John 20:22). It is only by this means that the church can offer forgiveness of sins, “If you forgive the sins of any, they are forgiven them; if you withhold forgiveness from any, it is withheld” (John 20:23). By church, I simply mean disciples of Jesus Christ who unite through the Spirit and thereby can offer forgiveness of sins by the same means (the Spirit).
The Acts of the Apostles records the work of the Spirit, converting and recreating hearts. From Pentecost forward, it becomes obvious that the good news becomes especially good because the Spirit perfects the work of the Son in accordance with the promise of the Father.
The Trinity Is the Gospel
In history, revelation comes progressively. In the words of Gregory of Nazianzus, the Old Testament clearly reveals the Father, the New Testament the Son, and the church the Holy Spirit. This approximates what I described above. In this sense, the Triune act (energeia) across history outlines the Gospel.
Incidentally, this explains why divine acts and not just covenants provide the backbone of the story of Scripture. Granted, covenants constitute some of the major acts of God. So I by no means intend to downplay covenants but rightly to define them. Covenants cannot replace metaphysics.
But the historical acts of God alone do not fully explain how the Trinity and the Gospel can both stand at the centre of our faith and really describe the same idea. For that, we need to turn to the inner life of God because the inner life of God bespeaks the Gospel.
By nature, God is good. He is love. In him is life, life eternal. It overflows in him in the dynamic, un-bounded life of God. God is the Father begetting the Son and spirating the Spirit. His life is these relations, apart from time or any created effect. God always loves the Son through the Spirit—with fullness.
Out of his supreme and dynamic goodness, he created the world and called it very good (Gen 1:31). Out of his supreme love and mercy, he sent his Son into the world to save it (John 3:16). For God so loved the world. He did. And he has. And the Son tells us that it is to our benefit that he goes so that he can send the Holy Spirit (John 16:7).
So the Gospel flows from the nature of God. The Good News is that God is. Out of his beneficence, he promises to love, save, and cherish his people. He gives us the best gift possible—himself: Father, Son, and Spirit.
The Gospel of God
Kevin Vanhoozer recently wrote, “biblical narrative raises questions only ontology can answer.” The narrative of the Good News, of Scripture, requires ontological answers—answers about who God is.
To say that Christ died, was buried, rose, and appeared according to Scripture demands ontological and metaphysical explanation. For the former, Paul does just that in Philippians 2:6–11. For the latter, John does that in his Gospel and Apocalypse.
The Gospel is God. The Good News is that God is. And because he is supreme goodness and love, God creates out of his goodness and redeems according to his love.
So Jesus, the only begotten God along with the triune Gospel stand at the centre of our faith. It just depends on how we look at the same idea. Do we look according to history or according to metaphysics? Of course, we can do both by affirming that the man Jesus Christ is both Lord and Saviour who fulfills the will of his Father and sends the Spirit.