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In this illuminating episode, we explore Westminster Shorter Catechism Answer 6, which addresses the doctrine of the Trinity. The episode traces how the early disciples came to understand that the one God of Israel exists as three persons—Father, Son, and Holy Spirit—who share the same divine substance and are equal in power and glory. Through biblical examples from both the New and Old Testaments, we see how this doctrine isn’t merely an abstract theological concept but the living reality of God’s nature that fundamentally shapes our understanding of salvation, worship, and the entirety of Scripture. The Trinity is presented not as a contradiction to be solved, but as a revealed mystery that helps us comprehend God’s eternal existence as a perfect, loving community.
Key Takeaways
- The Trinity consists of three distinct persons (Father, Son, and Holy Spirit) who are one God, sharing the same divine substance and equal in power and glory.
- The doctrine of the Trinity emerged from the disciples’ experiences with Jesus and the Holy Spirit, culminating in Peter’s Pentecost sermon as the first truly Trinitarian proclamation.
- The language of “substance” and “person” developed over centuries to articulate biblical truth, not as an invention of new doctrines.
- The unity of the divine substance means there can only be one omnipotence and one ultimate glory shared by all three persons.
- Romans 8 demonstrates the unified work of the Trinity in salvation: the Father predestines and justifies, the Son accomplishes salvation, and the Spirit applies it to believers.
- The Trinity provides interpretive clarity for previously mysterious Old Testament passages such as Genesis 1:26 (“Let us make man in our image”) and Psalm 110:1.
- The doctrine of the Trinity reveals that God has eternally existed as a perfect, loving community within Himself.
Key Concepts
The Trinity as Biblical Reality, Not Philosophical Invention
The episode emphasizes that the Trinity is not a later church invention but the lived experience of the first disciples. Peter and the others encountered the Father’s voice at Jesus’s baptism and the Transfiguration, witnessed Jesus claiming divine authority and unity with the Father, and experienced the Holy Spirit at Pentecost. This experiential reality preceded the formal language used to describe it. The church subsequently developed vocabulary to articulate and defend this revealed truth, using terms like “substance” (to describe God’s unified divine nature) and “person” (to describe the three distinct subsistences within that nature). This careful language serves as guardrails around biblical truth, preventing both the error of tritheism (three gods) and modalism (one God appearing in three modes).
The Trinity’s Perfect Unity and Distinct Operations in Salvation
Romans 8 offers perhaps the clearest biblical picture of how the three persons of the Trinity work in perfect harmony while maintaining their distinct operations in salvation. The Father initiates salvation through predestination, justification, and unchangeable love. The Son accomplishes salvation through his death and resurrection, removing condemnation and interceding at the Father’s right hand. The Spirit applies salvation by freeing believers from sin’s power, leading them as adopted children, and interceding for them in prayer. This shows that while the Trinity shares one divine substance, power, and glory, each person has distinct personal operations within God’s unified work. This pattern of Father planning, Son accomplishing, and Spirit applying extends throughout Scripture and forms the foundation of our understanding of how God saves his people.
Memorable Quotes
“The Trinity isn’t a contradiction to be solved, but a glorious, revealed mystery to be adored. It tells us that our God has eternally existed as a perfect, loving community within Himself.”
“The Old Testament may be likened to a chamber richly furnished but dimly lighted; the introduction of light brings into it nothing which was not in it before; but it brings out into clearer view much of what is in it but was only dimly or even not at all perceived before.”
Full Transcript
[00:00:07] The First Disciples’ Tension
On Tuesday, we entered into the story of the first disciples. We felt the profound tension they must have experienced as their rock-solid belief in the one God of Israel was confronted by the man Jesus, who claimed to be Yahweh, and then by the Holy Spirit, who came to dwell within them. We ended by asking the catechism’s unavoidable question: How many persons are there in the Godhead?
[00:00:32] The Church’s Answer to the Godhead
Today, we turn to the church’s historic, biblically-grounded, and Spirit-illuminated answer. There are three persons in the Godhead; the Father, the Son, and the Holy Ghost; and these three are one God, the same in substance, equal in power and glory.
Before we unpack the careful language of this answer, let’s return to our story.
[00:00:54] Peter’s Pentecost Experience
Imagine you are Peter on the day of Pentecost. The tension of the last few years has reached its peak. You’re huddled with the other disciples, and suddenly, you hear the rushing wind. You see the tongues of fire. You feel the promised Holy Spirit filling you, a divine, personal presence. And in that moment, your mind flashes back. You see the waters of the Jordan, and you remember Jesus’s baptism. The Father’s voice booming from heaven, declaring His love for His Son, as the Spirit descends like a dove. Your mind then shoots forward to the Mount of Transfiguration, seeing Jesus in his glory as the Father again speaks from the glory cloud, the very presence of the Spirit. Finally, you recall some of the last words Christ ever spoke to you on earth, his great commission to go and make disciples, baptizing them in the singular name of the Father, and of the Son, and of the Holy Spirit.
And it all clicks. The tension doesn’t break you; it resolves into a beautiful, glorious harmony. You take a deep breath, you step out onto the streets of Jerusalem, and you begin to preach the first truly Trinitarian sermon the world had ever heard.
That is the lived reality. Peter preached the experience of the Triune God.
[00:02:11] The Church’s Vocabulary Development
In the centuries that followed, the church had to develop a careful vocabulary to explain and defend that reality against those who would distort it. They didn’t invent new doctrines, but they did adopt and adapt existing words to serve as guardrails for this profound biblical truth. We’ll talk more about that next week when we dip our toes into the great creeds of the church.
[00:02:33] Understanding the Divine Substance
But for now, it’s enough to know that the language the church settled on to describe the way God is one was substance—His divine nature—and the way God is three was person.
This brings us to the second half of our answer. The Father, Son, and Holy Spirit “are one God, the same in substance, equal in power, and glory.” This isn’t an appendix; it’s the anchor that keeps the whole doctrine from drifting into error.
Think back to what we learned about the nature of God. We affirmed that He is infinite, eternal, and unchangeable. These are attributes of the divine essence, the divine substance. Therefore, if the Father, Son, and Spirit are all truly the one God, they must fully and equally share that one divine substance. This is precisely what Jesus himself claimed when he declared in John 10:30, “I and the Father are one.” He was not claiming to be the same person as the Father, but to share the same divine nature. There aren’t three separate consciousnesses or three parts of God. There is one, undivided divine essence, which subsists in three distinct persons.
From this, the rest logically follows.
[00:03:44] Unity in Power and Glory
They are equal in power. There can only be one omnipotence. If you had three separate, all-powerful beings, you wouldn’t have a Godhead; you would have chaos.
Jesus makes this clear in John 5:19 when he says that “whatever the Father does, that the Son does likewise.” This reveals a perfect unity of will and an equality of action, which can only come from an equality of power. Because the Father, Son, and Spirit are one in substance, they share one, single, infinite power. The power of the Son is the power of the Father. The power of the Spirit is the power of the Son.
And they are equal in glory. There can only be one ultimate glory, because there is only one being worthy of our ultimate worship. Jesus prayed to the Father in John 17:5, asking to be glorified “with the glory that I had with you before the world existed.” This shows us that the Son possessed a co-eternal glory with the Father, a glory that is inherent to the divine being. If the glory of the Father, Son, and Spirit were separate, our worship would have to be divided. But because they are one God, they share one glory. To glorify the Son is to glorify the Father. To be filled with the Spirit is to be brought into the glorious presence of the Father and the Son.
[00:05:03] Trinitarian Reality in the New Testament
We see this Trinitarian reality woven throughout the New Testament. In the Great Commission, Jesus commands us to baptize in the single “name”—not “names”—of the Father, the Son, and the Holy Spirit. One name, one divine essence, yet three distinct persons. But perhaps nowhere is the unified work of the Trinity more beautifully displayed for the life of the believer than in Romans chapter 8.
In that one chapter, Paul shows us the whole Godhead working in perfect harmony for our salvation. It is God the Father who predestines us, who justifies us, and from whose love nothing can separate us. It is God the Son, Jesus Christ, through whom we have no condemnation, who is at the Father’s right hand interceding for us, and in whom that love of the Father is made real. And it is the Holy Spirit who frees us from the law of sin and death, who leads us as sons, who testifies with our spirit that we are children of God, and who helps us in our weakness, interceding for us with groanings too deep for words. The Father plans and purposes our salvation. The Son accomplishes it on the cross and secures it at the right hand of the Father. The Spirit applies it to our hearts and seals us in it. One unified work of salvation, carried out by three distinct, divine persons.
[00:06:24] Old Testament Insights Through the Trinity
This Trinitarian understanding doesn’t just illuminate the New Testament; it shines a light backward, making sense of passages in the Old Testament that were once mysterious. The great Reformed theologian B.B. Warfield provided a perfect analogy for this. He said: “The Old Testament may be likened to a chamber richly furnished but dimly lighted; the introduction of light brings into it nothing which was not in it before; but it brings out into clearer view much of what is in it but was only dimly or even not at all perceived before.” Warfield argued that the mystery of the Trinity underlies the Old Testament, and here and there almost comes into view. The New Testament doesn’t correct the Old, but perfects and enlarges it.
This is exactly what we see. Think of Genesis 1:26, at the very moment of man’s creation, where God says, “Let us make man in our image.” For centuries, commentators wondered: who is the “us”? But through the lens of the Trinity, we see the beautiful truth: this is an intra-Trinitarian counsel. The Father, Son, and Holy Spirit, in their unified will, create mankind. The plurality within the Godhead was there from the very beginning. Jesus himself did this when he challenged the Pharisees with Psalm 110. He asked them how the Messiah could be both David’s son and David’s Lord, quoting the verse, “The LORD said to my Lord…” The Pharisees were silenced because their strict, unitarian framework couldn’t solve the riddle. But the Trinity does. There is the LORD, Yahweh the Father, speaking to “my Lord,” the divine Son. The Trinity isn’t a New Testament invention; it’s the key that unlocks the full counsel of God across both testaments.
[00:08:10] Conclusion: The Doctrine of the Trinity
This is the doctrine of the Trinity. It is not a contradiction to be solved, but a glorious, revealed mystery to be adored. It tells us that our God has eternally existed as a perfect, loving community within Himself. Our God is the Father who plans our redemption, the Son who accomplishes it, and the Holy Spirit who applies it to our hearts. He is one God, the same in substance, equal in power, and glory.