The Christian church has believed that Jesus was God for 2,000 years of its history. While the word “Trinity” is not found in the Bible, the Scripture that helped formulate that doctrine is found in the Bible.
Additionally, in response to a major controversy in the church, the Emperor Constantine called a church council in A.D. 325 at Nicaea to solve the controversy that was dividing the church. Some were teaching that Jesus was not fully human, and others were teaching that Jesus was not fully God.
Since the majority believed that both Scripture and church tradition taught that Jesus was both fully human and fully divine, the Doctrine of the Trinity was created as a response to what was believed to be erroneous teaching.
The Gospel of John presents Jesus as God as a main theme. This is true from the opening passage that presents Jesus as the living Word of God:
In the beginning was the Word, and the Word was with God, and the Word was God (John 1:1)
In John 10:30, Jesus said:
I and the Father are one.
This continues throughout the Book of John until the Disciple Thomas sees the resurrected Jesus and declares:
My Lord and my God! (John 20:28)
For a first-century Jew to declare that is monumental, for they fully believed in Deuteronomy 6:4-5:
Hear, O Israel: The Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your strength.
It was this belief in one God that set Israel apart from the rest of the world that believed in a multitude of gods.
This is a complex and confusing doctrine, and yet, at the same time, it is very simple. Our human mind just cannot comprehend how Jesus can be both fully human and fully God, and how God can be one and yet three.
However, God is a God of paradox, and we find paradox throughout creation, from the micro to the macro. We also find paradox through Scripture, such as if you want to be first, be last; if you want to live, then die; and many other apparently mutually exclusive statements.
While we do not understand how God can do these things, we should understand that if God is really God, then He is not bound by our limited understanding. As the God of creation that merely spoke everything into existence, including time, nothing is impossible for Him. Not even the Trinity.
There is only one God who is revealed in three persons as the Father, the Son and the Holy Spirit.