Christians are people of the book, but the word “Trinity” is not found anywhere in the Bible. So, is the Trinity a biblical doctrine? And if so, is it rational?
What Does the Bible Teach?
Though the Bible does not contain one verse that sums up the Trinity, it gives at least three distinct truths that are combined together to get the doctrine of the Trinity.
The Bible consistently states that there is only one God.
The truth that there is only one God is highlighted in the Old Testament, including the Shema that emphasizes the radical monotheism of the Jewish people (Dt 6:4-6). Isaiah contrasts the one true God, the only Savior, with the false gods of the surrounding peoples (Is 45:21-22; see also Is 40:21-26; 46:9-10). The New Testament teaches this truth as well, with Jesus repeating the command of Dt 6:5 as the greatest commandment (Matt 23:37-38) and James reinforcing the goodness of believing in one God (Jas 2:19a).
In light of this repeated and strong emphasis on the oneness of God, where did the idea of the Trinity come from? When we look through the Old Testament, the doctrine of the Trinity is implied through the use of plural pronouns in reference to God (Gen 1:26; Gen 3:22; Gen 11:7; Is 6:8), references to two persons both described as God (Ps 45:6-7; Ps 110:1; Is 48:16; Is 63:10), and accounts of the angel of the Lord (Gen 16:7-11; 22:11-15; Num 22:16-35).
However, when we come to the New Testament the idea of the Trinity is already firmly in place, undergirding all of what we find there. For example, in Paul’s earliest letter—1 Thess 1:2-6—he opens with a reference to the work of the Father (choosing), the Son (offering hope and providing an example) and the Spirit (working with the Word and producing joy) without any need to explain who these three persons are. Additionally, the very first sermon of the church age includes a clear Trinitarian understanding (Acts 2:38-39).
What happened? The apostles met Jesus and saw that he was God, and they experienced the reality of the Holy Spirit coming at Pentecost. They knew that God was Triune, so their teaching was built on that reality. They worshipped God the Father, God the Son, and God the Holy Spirit. The writings of the NT help us to understand more of what it means to say that God is Triune.
The Bible teaches that the Father is God, the Son is God, and the Spirit is God
The Father is clearly identified as God (John 6:27; John 17:3; Gal 1:3).
Jesus’s divinity is assumed in his ego-centrism. For someone to talk like he did and not be God would be lunacy. His words are the foundation for living (Matt 7:24-27). He determines who will know the Father (Matt 11:27). People must forsake all to follow him (Matt 16:25). He has angels (Matt 13:41; 16:27; 24:31). He rewards and punishes men (Matt 16:27-28; 25:31-46). He calls people to forsake their family for him (Lk 14:26; Matt 10:37).
No OT prophet ever drew attention to himself in this way, claiming to be the source of all divine blessing and the standard of all divine judgment. Godly teachers typically turn attention away from themselves and point people to God. If Jesus is not God, his egocentric teaching is prideful—even blasphemous. Only if he is God is it admirable. (John Frame, The Doctrine of God p. 648)
You can’t read the NT honestly without recognizing that it teaches that Jesus is God.
Additionally, there are several verses that directly state that Jesus is God. (Jn 1:1; 18; 20:28; Acts 20:28; Rom 9:5; 1 Tim 3:15–16; 2 Thess 1:12; Tit 2:13; 2 Pet 1:1; Heb 1:8; 1 Jn 5:20).
The Spirit is also recognized as God. Peter equates the Holy Spirit with God (Acts 5:3-4). The Spirit is coeternal and coequal with the Father and the Son (Mt 28:19; Heb 9:14). He possesses the divine attributes such as omniscience (1 Cor 2:10-11), omnipresence (Ps 139:7-11), omnipotence (Lk 1:35), eternality (Heb 9:14), holiness (Eph 4:30), truth (1 Jn 5:7), life (Rom 8:2), and love (Rom 15:30). He is not merely a force but is a person, as is demonstrated by the traits of personality he possesses such as the ability to teach (John 16:13), to convict (16:8), to comfort (John 15:26), to be blasphemed (Matt 12:31) and to be grieved (Eph 4:30).
The Bible teaches that the Father, Son, and Spirit are distinct
The Bible does not portray the Father, Son, and Spirit as different roles of the one God, as though He were putting on different hats or temporarily becoming different persons. Instead, they are distinct persons. Jesus asks the Father to send the Spirit, another comforter (John 14:16). Jesus is with God while at the same time being God (John 1:1-2). Jesus loves the disciples (different persons) as the Father loves the Son (John 15:9). All three persons appear separately at Jesus’ baptism (Matt 3:16-17).
Is the Trinity Rational?
Some critics object to the idea of the Trinity itself. The Bible might teach something like this, they argue, but perhaps that just shows that the Bible is flawed. After all, 1+1+1 equals 3, not 1, so how can you really claim to only worship one God. You actually worship three.
First, it is important to see that the Trinity is not inherently illogical. Christians do not believe that God is one and God is three in the same way. God is one being and three persons, not one being and three beings or one person and three persons. Our being is not capable of having more than one person, but God’s is.
Which leads to the second point—even if we can recognize what the Trinity is stating and see that it is not illogical, that does not mean that we can fully comprehend it. There is a mystery about the Trinity. We could not understand God on our own, but we can understand as much as possible, what He has revealed about Himself (Dt 29:29).
The tendency to reject the Trinity flows from a desire to have a god we can fully comprehend. But that god is no greater than we are. The God of the Bible is far greater than us, which means we cannot fully comprehend Him. This helps us see why most analogies for the Trinity actually fail, because they are seeking to compare something to God when God is not like anything else. He is unique!
So the Trinity is biblical and logical, even though we cannot fully comprehend it. But we are not required to fully comprehend it. Rather, we are called to believe what God has said and respond in worship and obedience to the Triune God.