CHAPTER 5 · WEEK 5 How Can God Be Three and One? Theology Proper II — the Holy Trinity |
WHAT WE BELIEVE There is one God in three Persons — the Father, the Son, and the Holy Spirit — equal in deity, distinct in person, undivided in essence. This is not a puzzle to solve but a glory to confess. The gospel, Christian worship, and Christian prayer are Trinitarian or they are not Christian. |
Learning Aims for This Week
By the end of this chapter you should be able to:
· State the biblical case for one God, three distinct Persons, and the full deity of each.
· Use historic language (essence, person) carefully and know why it was needed.
· Identify modalism, Arianism, and tritheism.
· Explain why the Trinity is essential to salvation and worship.
Key Terms
Term | Meaning in this course |
Trinity | The church’s word for the biblical teaching that God is one in essence, three in Person. |
Essence / substance | What God is — the one divine being. |
Person | Who God is as Father, Son, and Spirit — distinct, not three gods. |
Eternal generation | The Son is begotten of the Father eternally, not made. |
Procession | The Spirit proceeds from the Father (and, in Western confession, from the Son). |
Modalism | The error that Father, Son, and Spirit are only masks or modes of one Person. |
Arianism | The error that the Son is a created being, not fully God. |
Tritheism | The error that there are three gods. |
Economic Trinity | God as He acts in creation and redemption. |
Immanent Trinity | God as He is in Himself — Father, Son, and Spirit eternally. |
Teaching Notes
1. The word is later; the teaching is biblical
You will not find the word Trinity in Scripture. You will find the reality everywhere. Israel’s Shema is non-negotiable: “The Lord our God, the Lord is one” (Deut. 6:4). Yet the Father sends the Son; the Son prays to the Father and promises another Advocate; the Spirit is lied to and is called God (Acts 5:3–4). Baptism is into the one Name of the Father and of the Son and of the Holy Spirit (Matt. 28:19). The apostolic blessing is Trinitarian (2 Cor. 13:14).
2. Three claims that must all stay true
1. There is only one God.
2. The Father, the Son, and the Spirit are each fully God.
3. The Father, the Son, and the Spirit are distinct Persons, not interchangeable masks.
Drop the first and you have three gods. Drop the second and you have a created Jesus or an impersonal Spirit. Drop the third and you have a God who only pretends to be three. Historic Christianity refuses all three reductions.
3. The Son and the Spirit are God
John 1:1–3, 14: the Word was God, was with God, and became flesh. John 20:28: “My Lord and my God!” Colossians 1:15–20; 2:9; Hebrews 1:1–4; Titus 2:13. The Spirit is personal (He speaks, can be grieved) and divine (1 Cor. 2:10–11; Heb. 9:14). The church did not upgrade Jesus at Nicaea. Nicaea refused to downgrade Him.
4. Why the Trinity is not an extra credit unit
The Father plans redemption, the Son accomplishes it, the Spirit applies it — one work of the one God. If the Son is not God, the cross is not God-with-us and cannot reconcile us to God. If the Spirit is not God, the indwelling of the Spirit is not the indwelling of God. We pray to the Father, through the Son, in the Spirit. We are baptized into the Triune Name. Christian life is communion with the three-personal God.
Illustrations almost always fail. Water / ice / steam is modalism. A three-leaf clover is often tritheism or a division of parts. Use illustrations sparingly, then take them back. Better to say: God is like a Father with a Son, and the Spirit is the living bond of their love — and even that is only a pointer. |
Key Scriptures
Read these passages slowly before class. Mark what they teach about this week’s doctrine.
· Deuteronomy 6:4–5 — The Lord is one.
· Matthew 3:16–17 — The baptism of Jesus: Father, Son, and Spirit together.
· Matthew 28:18–20 — Memory verse: one Name, three Persons, one mission.
· John 1:1–18 — The Word was God and became flesh.
· John 14:16–17, 26 — Another Advocate.
· 2 Corinthians 13:14 — The Trinitarian blessing.
· Ephesians 1:3–14 — The Father elects, the Son redeems, the Spirit seals — one sentence of praise.
For Discussion
· Why do illustrations of the Trinity so often become heresies?
· How does John 1:1 hold together “the Word was with God” and “the Word was God”?
· What happens to prayer if we forget one of the Persons?
· How would you help a new believer who says, “The Trinity doesn’t make sense, so I ignore it”?
Personal Application
· Pray one prayer this week deliberately to the Father, through the Son, in the Spirit.
· Memorize Matthew 28:18–20.
· Read the Nicene Creed slowly. Mark every phrase that is about the Son.
This Week’s Work
· Read the assigned Grudem pages on the Trinity.
· Write, without notes, the three claims that must all stay true. Check yourself.
· Doctrine Brief #1 due soon if that is your topic.
A Prayer to Carry into the Week
Father, I praise You. Son of God, I praise You. Holy Spirit, I praise You. One God, ever to be worshiped. Keep me from shrinking this glory into a diagram. Lift my heart into the communion You have made. Amen.
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