The Nicea Creed.
325 AD. The council of Nice, Convoked by Constantine the great by the advice of Alexander, Bishop of Amexandria. at the council of all the bishops of Asia, Africa and Europe. The object of the council was to refute the teaching of Arius a presbyter of Alexandria who denied the divinity of Jesus Christ. They concluded that from eternity there were three divine persons, Father, Son and Holy Spirit. A creed was made and written as follows. I Believe in one God the Father Almighty maker of heaven and earth; and in the one Lord Jesus Christ the only begotten son of God, being of one substance with the father, who came down from heaven and was incarnate by the Holy Ghost of the Virgin Mary; and in the Holy Ghost the Lord and giver of life who proceedeth from the Father and the Son, who was with the Father and the Son together is worshipped and glorified.
In the Athenasian creed it is said; This is Catholic faith, that we worship one God in trinity,, and trinity in unity, never confounding the persons, nor dividing the substance, for there is one person of the Father, another of the Son, and another of the Holy Ghost. The Athanasian creed was composed immediately after the council of Nicea by one or more of those present (The True Christian Religion by Emanuel Swedenborg p670/671 1933)
As stated each person is believed to be God. They have made one God of three, but not one person of three. Hence the error. Three divine persons from eternity. The son made an eternal son. How different from the doctrine of the incarnation, that God himself took on flesh and so being found in fashion as a man humbled himself other death of the cross (Phil 2;8; 1 Tim 3;16).
Wikipedia: the doctrine of the incarnation holds that Jesus, the preexistent divine Logos (Koine Greek for "Word") and the second hypostasis of the Trinity, God the Son and Son of the Father, taking on a human body and human nature, "was made flesh" (Wikipedia) Again the trinitists twist the teaching of the incarnation, to suggest that the Son as a person came from eternity and took on a body. The Bible clearly teaches however that It was not an eternal Son that came, but he who was God that came. God was made flesh and as a man was only known as the Son. His office of Son was temporal and for this reason. For this reason was the Son of God manifest that he might destroy the works fo the evil one. (1 John 3;8). The office of sonship was temporal, yet he as God is from everlasting to everlasting both the Alpha and Omega, the mighty God (Rev 22;13 Isaiah 9:6)