In the fourth century,
Arianism, as traditionally understood,
[c] taught that the Father existed prior to the Son who was not, by nature, God but rather a changeable creature who was granted the dignity of becoming "Son of God".
[65] In 325, the
First Council of Nicaea adopted the Nicene Creed which described Christ as "God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father", and the "Holy Ghost" as the one by which "
was incarnate... of the
Virgin Mary".
[66][67] ("the
Word was made flesh and dwelled among us"). About the Father and the Son, the creed used the term
homoousios (of one substance) to define the relationship between the Father and the Son. After more than fifty years of debate,
homoousios was recognised as the hallmark of orthodoxy, and was further developed into the formula of "three persons, one being".
The Confession of the First Council of Nicaea, the Nicene Creed, said little about the Holy Spirit.
[68] At the First Council of Nicea (325) all attention was focused on the relationship between the Father and the Son, without making any similar statement about the Holy Spirit. In the words of the creed:
We believe in one God, the Father Almighty, Maker of all things visible and invisible. And in one Lord Jesus Christ, the Son of God, begotten of the Father [the only-begotten; that is, of the essence of the Father, God of God,] Light of Light, very God of very God, begotten, not made, being of one substance with the Father; ... And [we believe] in the Holy Ghost. .