Reading Systematic Theology with Wayne Grudem – How can God be three persons, yet one God?

This post is part of a 50+ post series from the classic work by Wayne Grudem (PhD, Cambridge), Systematic Theology: An Introduction to Biblical Doctrine. The aim of each post is to provide an overview of each chapter in the book and related resources for each topic.

Synopsis of Chapter

In this chapter of Systematic Theology, Grudem tackles the concept of the Trinity. The doctrine of the Trinity affirms that God is one God who exists in three persons – the Father, Son, and Holy Spirit. He examines how this doctrine is found in both the Old and New Testaments and identifies three simple statements that summarize the biblical data:

  1. God is three persons.
  2. Each person is fully God.
  3. There is one God.

In addition to the positive statements, Grudem examines the major errors the church has rejected about the nature of God. He examines some of the biblical distinctions between the persons of the Trinity. Finally, he ends with an application section explaining why this doctrine is important. 

The Scriptural Basis for the Trinity

The Bible progressively reveals the doctrine of the Trinity. Starting with the first chapter of Genesis, Scripture declares, “Then God said, ‘Let us make man in our image, after our likeness.’” (Genesis 1:26a). This passage clearly denotes a plurality in God, though it would be many hundreds of years before God’s people were to have a more clear understanding of what it meant. 

The New Testament begins to clarify this plurality in God with the incarnation of Jesus. Some passages point to the Holy Spirit’s connection to the Father and the Son like at Jesus’ baptism (Matthew 3:16-17). In 2 Corinthians 13:14, we see all three members of the Trinity connected, “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.” There are a few passages that connect all members of the Trinity, but the argument for the Trinity is more robust than simple proof texts.

God Is Three Persons

The first of the three summary statements on the Trinity is: God is three persons. In other words, the Father is not the Son, and the Holy Spirit is not the Father – each member is a separate person. John 1:1 distinguishes between the Father and the Son (“the Word was with God”). John 14:26 describes how the Father will send the Holy Spirit thus distinguishing between their persons. Even Jesus sends the Holy Spirit (John 16:7) which means they are not same. 

Though the Spirit is sometimes not considered God by certain religious groups, there are many reasons to affirm the deity of the Holy Spirit. He is referred to in the masculine pronoun (John 14:26, 15:26), he is ascribed personal activities like teaching (John 14:26), he searches the depths of God (1 Cor 2:10), and speaks (Acts 8:29). God is three persons and the Holy Spirit is one of the persons of the Godhead.

Each Person is Fully God  

The second statement about the Trinity is each person is fully God. God, the Father, is fully God along with God the Son, and God the Holy Spirit. Few people will argue with the deity of God the Father. He is viewed as the Sovereign over all creation in the Old and New Testaments. 

God the Son is also fully God. John 1:1 declares, “In the beginning was the Word, and the Word was with God, and the Word was God.” In this and other verses, the Apostle John makes clear that Jesus was God. He even culminates his gospel record about ‘Doubting’ Thomas who declared to Jesus, “My Lord and my God.” (John 20:27). 

The Holy Spirit is also fully God. In Acts 5:3-4, Peter equates lying to the Holy Spirit as lying to God. David also attributes omnipresence with the Holy Spirit in Psalm 139:7-8 when he asks, “Where shall I go from your Spirit? Or where shall I flee from your presence? If I ascend to heaven, you are there! If I make my bed in Sheol, you are there!” So the Holy Spirit is God just as much as the Father and the Son.

There Is One God

The third and final statement on the Trinity is there is one God. One of the more familiar passages in the Old Testament is Deuteronomy 6:4, “Hear, O Israel: The Lord our God, the Lord is one.” God is one, not many. Paul reaffirms the Old Testament teaching on the unity of God when he says “there is one God” (1 Timothy 2:5) and “God is one.” (Romans 3:30). The oneness of God is an established aspect of the Trinity that Christians have affirmed since the days of the ancient church.

Anti-Trinity: Modalism Claims There’s One Person in Different “Modes”

There are several historic deviations from the doctrine of the Trinity. The first one is modalism. Modalism, also called “modalistic monarchianism” or “Sabellianism,” is the idea that denies the separate persons in the Trinity. They taught that God is one being who shows himself in three forms so it denies the separate personhood of the Gather , Son, and Holy Spirit. To Modalists, God is the same God who exists in three “modes”, hence the term Modalism.

Anti-Trinity: Arianism Denies the Full Deity of the Son and the Holy Spirit

Another challenge to the Trinity came from the followers of Arius, Bishop of Alexandria. Arius and his followers taught that Jesus was a created being and not God. They appealed to the certain texts referring to Jesus as “begotten” and so he could not be eternal.

In A.D. 325, the Council of Nicea condemned Arianism for denying the deity of Jesus. The majority of the church could not accept the idea that Jesus was merely a created being and so they were eventually driven outside of the main body of believers and eventually died out. The group that bears some semblance to the ancient Arians are Jehovah’s Witnesses. Their group also denies the deity of Christ.  

There were other teachers that denied the full deity of Jesus. Subordinationism is similar to Arianianism in that they denied the full deity of Jesus. They believed that the Father was greater than the Son and the Son was therefore subordinate to the Father. Another similar error was Adoptionism. Adoptionists believed that Jesus was just a man until his baptism. At his baptism, the Father ‘adopted’ him as his Son and he became the Savior. All of these Arian-like heresies were ultimately rejected in the 4th century at the Council of Constantinople (AD 381). 

Application: The Importance Of The Doctrine Of The Trinity

The Trinity is of utmost importance in our understanding about God. Who else but God can die for the sins of people. If Jesus was just another creature, how could he save us? And how could we trust him, a supposed mere mortal, to save us if he were not fully and eternally God?  

In addition, the Trinity affirms both the unity and diversity in God. He is both unified (“the LORD is one” – Deuteronomy 6:4b) and diverse (“let us make man in our image” – Genesis 1:26a). He is three persons yet he is just one God. The aspects of unity and diversity are seen in marriage. In marriage, people can be unified as a couple, yet diverse as separate people (Genesis 2:24). The Trinity is also demonstrated in the diversity and unity of the body of Christ. For we have “many members” yet we are still “one body” (1 Corinthians 12:12). In the same way we see unity and diversity on earth, we see it perfectly demonstrated in God as the Trinity.

“And when Jesus was baptized, immediately he went up from the water, and behold, the heavens were opened to him, and he saw the Spirit of God descending like a dove and coming to rest on him; and behold, a voice from heaven said, “This is my beloved Son, with whom I am well pleased.” (Matthew 3:16-17)

Special Terms

  • adoptionism
  • Arianism
  • economy subordination
  • eternal begetting of the Son
  • eternal generation of the Son
  • filoque
  • homoiousios
  • homoousios
  • modalism
  • modalistic monarchianism
  • only-begotten
  • ontological equality
  • Sabellianism
  • subordinationism
  • Trinity
  • tritheism 

Resources: Wayne Grudem

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