What Scripture says
The word “Trinity” isn’t in the Bible, but the teaching it names draws together several lines of Scripture:
1. There is one God. “Hear, O Israel: The Lord our God, the Lord is one” (Deuteronomy 6:4, ESV). “I am the Lord, and there is no other, besides me there is no God” (Isaiah 45:5). Jesus affirmed this (Mark 12:29), and so did Paul: “there is no God but one” (1 Corinthians 8:4).
2. The Father is God. “There is one God, the Father” (1 Corinthians 8:6).
3. The Son is God.
- “In the beginning was the Word, and the Word was with God, and the Word was God” (John 1:1).
- Thomas calls the risen Jesus “My Lord and my God!” (John 20:28).
- Paul calls Christ “God over all, blessed forever” (Romans 9:5), and Titus 2:13 speaks of “our great God and Savior Jesus Christ”.
- Hebrews 1:8 applies Psalm 45:6 to the Son: “Your throne, O God, is forever and ever.”
4. The Holy Spirit is God. Peter tells Ananias that lying “to the Holy Spirit” is lying “to God” (Acts 5:3–4). The Spirit has personal qualities: he teaches (John 14:26), can be grieved (Ephesians 4:30) and intercedes (Romans 8:26–27).
5. They are distinct. At Jesus’ baptism, the Son is baptized, the Spirit descends, and the Father speaks (Matthew 3:16–17). Jesus prays to the Father (John 17) and promises to send “another Helper”, the Spirit (John 14:16).
6. They are named together. “Baptizing them in the name [singular] of the Father and of the Son and of the Holy Spirit” (Matthew 28:19). “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all” (2 Corinthians 13:14).
What the evidence says
Interpretation
What the doctrine says
The Trinity holds all six points together: one God, eternally existing as three persons, the Father, the Son and the Holy Spirit, each fully God, sharing one divine nature, yet distinct from one another.
It is not:
- Three gods (tritheism), which would deny point 1.
- One person in three roles or modes (modalism), as if God were sometimes Father, sometimes Son, which would deny point 5. Jesus praying to the Father would make no sense.
- A hierarchy of divine and lesser beings (Arianism), which would deny points 3 and 4.
Hints in the Old Testament
Christians see hints of plurality in the Old Testament, though they would not have been read this way before Christ:
- “Let us make man in our image” (Genesis 1:26).
- The “angel of the Lord” who speaks as God himself (Genesis 16:7–13, Exodus 3:2–6).
- God’s Word and Spirit as active in creation (Psalm 33:6, Genesis 1:2).
History
Developing the language
The early church needed words to express what Scripture taught:
- Theophilus of Antioch (c. AD 180) used the Greek word trias (“triad”) for God, his Word and his Wisdom.
- Tertullian (c. AD 213) first used the Latin trinitas and the formula “one substance, three persons”.
- The Council of Nicaea (AD 325) affirmed against Arius that the Son is “of one substance” (homoousios) with the Father, “true God from true God”.
- The Council of Constantinople (AD 381) affirmed the full divinity of the Holy Spirit.
So the councils didn’t invent the Trinity; they defined it in response to challenges. The belief was present much earlier in Christian worship, such as baptism in the triune name (Didache 7, c. AD 100; see 3B.25) and prayer to Jesus (see 6.4).
Non-Trinitarian views
Some groups reject the Trinity, including Jehovah’s Witnesses, who hold the Son was created; Oneness Pentecostals, who hold a form of modalism; and Unitarians. They argue the doctrine is a later Greek philosophical development not found in Scripture. Trinitarians reply that the doctrine is the best way to hold together all the biblical data without dropping any of it.
Constantine
A popular claim is that Emperor Constantine invented the Trinity at Nicaea. He called the council, but the bishops, not Constantine, debated and decided the issue, and the belief long predated him (see 11.10).
Where they meet
The word isn’t in the Bible, but the teaching is: one God, with the Father, Son and Spirit each divine and distinct. The doctrine of the Trinity is the church’s attempt to hold together everything Scripture says.
What’s still open
How best to express the relationships within the Trinity. Theologians continue to discuss this.
Bottom line
The word isn’t in the Bible, but the teaching is: one God (Deuteronomy 6:4), with Father, Son and Spirit each divine (Matthew 28:19, John 1:1, Acts 5:3–4). This is rated Settled.