Trinity 3: Homoousios
The doctrine of the Trinity was really born out of the defense against heresy. Tertullian stated tres personae, una substantia to defend against Monarchianism, but it did not end there.
Arius, a great teacher and priest in the church in Alexandria in the early 4th century, wanted to protect the transcendence and uniqueness of God, and in doing so, began to teach the heresy of subordinationism (the idea that the Son is somehow less than the Father). Arius believed that God was unbegotten, eternal, and separated from the world, but Christ is not of the same essence as God, for Arius feared that would mean there are two gods. Instead, Arius claimed that Christ was the first creation of God, created before the creation of the world, and through whom God created the world. But Christ was not co-eternal with God, Christ was created. And as a creation of God, Christ cannot be one with God.
Athanasius, the bishop of Alexandria and contemporary of Arius, argued against Aruis, claiming that Christ’s divinity was necessary for salvation. In Arian soteriology, salvation comes through conforming our wills to the will of God through the example of Jesus. Athanasius argued that if Jesus is not fully God, we do not truly receive salvation, for only God can truly save. If Christ was only a creature, how could Christ be the way to salvation?
Athanasius’ position was established as the orthodox position of the church at the Council of Nicea in 325. The Council of Nicea was the first of several ecumenical councils in the early church, where the whole church attempted to establish theological agreement through assemblies of representatives. The Nicene Creed came out of the Council of Nicea, which states:
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 [homoousios] with the Father;
(But those who say: ‘There was a time when he was not;’ and ‘He was not before he was made;’ and ‘He was made out of nothing,’ or ‘He is of another substance’ or ‘essence,’ or ‘The Son of God is created,’ or ‘changeable,’ or ‘alterable’—they are condemned by the holy catholic and apostolic Church.)
So, by 325 the church had settled upon Christ as co-eternal with God, divine as God is divine, and of the same substance of God (homoousios).
Athanasius used the same soteriological argument to argue the divinity of the Holy Spirit. The Holy Spirit is necessary for salvation but only God can save, so therefore the Holy Spirit must be divine. It is the Holy Spirit that enters into us in salvation and brings us into community with God. As Athanasius said, “If we are made sharers of the divine nature through our partaking of the Spirit, it would be only a madman who would say that the Spirit is of created nature and not of the nature of God.”
The second ecumenical council of the church, the Council of Constantinople in 381, established the divinity of the Holy Spirit. The assembly edited the Nicene Creed and added the following about the Holy Spirit:
And in the Holy Ghost, the Lord and Giver of life, who proceedeth from the Father, who with the Father and the Son together is worshiped and glorified, who spoke by the prophets.
This clause, that the Holy Spirit proceeded from the Father, established the divinity of the Holy Spirit and the homoousios of the Holy Spirit with the Father.
So, there you have it, by 325 we all agreed that Christ was divine and of the same substance, homoousios, with God. And by 381 we all agreed that the Holy Spirit was divine and of the same substance, homoousios, with God. Not much more to debate any more, right? But, although the councils declared the full divinity of the Son and Holy Spirit with the Father, they did not answer how exactly these Three are all One God…