The Trinity is Christianity’s most unique, defining, incomprehensible, and awesome mystery. It is the revelation of who our Almighty Creator actually is—not just a god, but an infinite Being existing in eternity as three co-equal, infinite Persons, consubstantial yet distinct. The origin of the doctrine of the Trinity is the Bible, although the word Trinity is not used in the Bible.
As all orthodox Christians agree, the doctrine of the Trinity holds that God is one essence but three Persons; God has one nature, but three centers of consciousness; God is only one What, but three Whos. Some unbelievers mistakenly call this a contradiction. Rather, the doctrine of the Trinity is a mystery revealed by God in His Word. A contradiction would be to claim that God has only one nature but also three natures, or that He is only one Person but also three Persons.
From the very beginning of the church, Christians have understood the mystery of the Trinity, even before they began using the term Trinity.
For example, the first Christians knew the Son was the Creator (John 1:1–2), the “I Am” of the Old Testament (Exodus 3:14; John 8:58), equal to the Father (John 14:9), and the Judge of all the earth (Genesis 18:25; John 5:22), who is to be worshiped as only God is allowed to be (Deuteronomy 6:13; Luke 4:8; Matthew 14:33).
The first Christians knew the Holy Spirit was a separate Person with His own thoughts and will (John 16:13), who intercedes for us with God (Romans 8:27), proving He is a distinct Person from God the Father—since intercession requires at least two parties (no one intercedes with himself). Furthermore, a human can be forgiven for blaspheming God the Son, but not for blaspheming God the Holy Spirit (Matthew 12:32).
New Testament writers mention all three Persons of the Trinity together numerous times (e.g., Romans 1:4; 15:30; 2 Corinthians 13:14; Ephesians 1:13–14; 1 Thessalonians 1:3–6). The early believers knew that the Father and the Son sent the third Person of the Trinity, the Holy Spirit—“another counselor”—to live in our hearts (John 14:16–17, 26; 16:7). These mysteries were accepted fully by the early church as revealed truth, yet without the label of “the Holy Trinity.”
The Old Testament gave glimpses of the Trinity, and no passage of Scripture contradicts the doctrine. For example, in Genesis 1:26 God says in the plural, “Let us make mankind in our image.” God declares that He was completely alone when He created everything, stretching out the heavens and spreading out the earth “by myself” (Isaiah 44:24). Yet Jesus was the instrument of God’s creation (John 1:1–3; Colossians 1:16), in the company of the Holy Spirit who was hovering over the primordial waters (Genesis 1:2). Only the doctrine of the Trinity can explain it all.
The Torah hinted at the idea of God existing in multiple Persons and predicted His coming in the flesh. The Old Testament is filled with references to a coming world ruler (Genesis 49:10) to be born in Bethlehem (Micah 5:2), who was not only God’s Son (Isaiah 9:6) but a Messiah who would be God in the flesh (Isaiah 7:14; Zechariah 2:8–11). But the Jews were looking for—and, under Roman occupation, desperately hoping for—a triumphant, conquering Messiah, not a lowly, suffering Servant (Isaiah 53). Israel failed to recognize the Son of God due to His ordinariness (Isaiah 53:2; Matthew 13:54–58; John 10:33), and they killed Him (Zechariah 12:10; Acts 2:36).
In the years after the death of the last apostle, John, there were many attempts by Christian theologians to define and explain God to the church. Explanations of spiritual reality to earthly beings will always fall short; some teachers’ explanations were a bit off, while others sank into heresy. The errors put forward in post-apostolic times ranged from Jesus being all God and only appearing to be human (Docetism), to His being created rather than eternal (Adoptionism, Arianism, and others), to there being three separate gods in the same family (Tritheism), to the one God playing three different roles at different times (Modalism, Monarchianism).
As no religion can exist without knowing who or what its followers worship, there was a great need to define God in a way that all followers of Christianity would agree upon as “official” or orthodox doctrine. And, if Jesus were not God, all Christians were heretics for worshiping a created being.
It seems that the church father Tertullian (AD 160–225) was the first to apply the term Trinity to God. Tertullian uses the term in Against Praxeus, written in 213 to explain and defend the Trinity against the teaching of his contemporary Praxeus, who espoused the Monarchian heresy. From there, we can jump forward over a century of church discussion, schisms, and debate to the Council of Nicea in 325, when the Trinity was finally confirmed as official church doctrine.
A final observation. Theology is the attempt by flawed humans to understand the words of the Bible, just as science is the attempt by flawed humans to understand the facts of nature. All the facts of nature are true, just as all the original words of the Bible are true. But humans are limited and make lots of mistakes, as history continually shows. So, where there is error or disagreement in science or theology, both disciplines have methods of correction. The history of the early church reveals that many sincere Christian believers “got it wrong” when it came to defining God’s nature (a great lesson on the need for humility). But, through a careful study of God’s Word, the church was finally able to articulate what the Bible clearly teaches and what they knew to be true—God exists as an eternal Trinity.