The “first” ecumenical council “Council of Nicaea” estabablished the Nicene Creed. Which is the relationship of Jesus Christ to God the Father. The Trinity is further defined through Bible.
The list of Christian Churchs who follow the Trinity as a main belief in salvation is long, it would be easier to address those who don’t. They in fact practice heresy.
Isaiah 48:16-17 Come ye near unto me, hear ye this; I have not spoken in secret from the beginning; from the time that it was, there am I: and now the Lord GOD, and his Spirit, hath sent me.
Thus saith the LORD, thy Redeemer, the Holy One of Israel.
John 1:1 “the Word was God" “And the Word was made flesh"
Acts 20:28 declares that God purchased the church with His own blood. Therefore, Jesus is God!
Colossians 1:15-17
The Apostle Paul tells us that Jesus “…is the image of the invisible God, the firstborn of every creature: For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him: And he is before all things, and by him all things consist.”
John 8:58 "I say unto you, Before Abraham was, I am. "
John 10:30 “I and my Father are one.”
John 14:9 “he that hath seen me hath seen the Father”