The Ecumenical Councils and Creeds

The first five centuries of Christianity were marked by intense theological debate about the nature of God, the person of Christ, and the relationship between the divine and the human. These debates were resolved — or at least formally settled — by a series of ecumenical councils: gatherings of bishops from across the Christian world that defined orthodox doctrine and condemned heresy. The creeds produced by these councils remain foundational statements of Christian belief to this day.

The Arian Controversy

The most significant theological crisis of the early Church was the Arian controversy. Arius (c. AD 256–336), a priest in Alexandria, taught that the Son of God (the Logos, or Word) was a created being — the first and greatest of God’s creatures, but not eternal and not truly God. Arius argued:

There was a time when the Son did not exist — ‘there was when he was not’
The Son was created by the Father out of nothing (ex nihilo)
The Son is of a different substance (heteroousios) from the Father
The Son is divine in a subordinate, derivative sense — divine by grace, not by nature

Arius’s teaching was vigorously opposed by Athanasius (c. AD 296–373), who argued that if the Son is not truly God, then salvation is impossible. Only God can save; if Christ is merely a creature, however exalted, he cannot bridge the infinite gap between God and humanity. Athanasius insisted that the Son is homoousios — of the same substance as the Father — eternally begotten, not made.

Key Definition: Homoousios — Greek for ‘of the same substance’ or ‘of one being’. This term, enshrined at the Council of Nicaea, affirms that the Son shares the identical divine nature as the Father. It was the decisive term in the defeat of Arianism.

The Council of Nicaea (AD 325)

The First Council of Nicaea was convened by Emperor Constantine I and was the first ecumenical (‘universal’) council of the Christian Church. Approximately 318 bishops attended. The council’s primary purpose was to resolve the Arian controversy.

The council produced the Nicene Creed, which affirmed that the Son is:

‘God from God, Light from Light, true God from true God’
‘Begotten, not made’ — the Son is eternally generated from the Father, not created
‘Of one being (homoousios) with the Father’ — the Son shares the identical divine substance
‘Through him all things were made’ — the Son is the agent of creation, not part of creation

The council explicitly condemned Arianism, declaring that those who say ‘there was when he was not’ or that the Son is ‘of a different substance’ from the Father are anathematised (formally condemned) by the Catholic and Apostolic Church.

The Council of Nicaea also addressed several practical matters, including the date of Easter, the readmission of lapsed Christians, and the precedence of the major episcopal sees (Rome, Alexandria, Antioch).

The Council of Constantinople (AD 381)

The First Council of Constantinople, convened by Emperor Theodosius I, reaffirmed the Nicene faith and extended the creed to address the divinity of the Holy Spirit. The Pneumatomachi (‘Spirit-fighters’) had denied that the Holy Spirit was fully divine. The council affirmed that the Holy Spirit is:

‘The Lord, the giver of life’
‘Who proceeds from the Father’
‘Who with the Father and the Son is worshipped and glorified’
‘Who has spoken through the prophets’

The expanded creed — known as the Niceno-Constantinopolitan Creed — is the creed recited in most Christian churches today. It represents the definitive Trinitarian statement: one God in three persons — Father, Son, and Holy Spirit — co-equal, co-eternal, and of one substance.

A later addition to this creed — the Filioque clause (‘and the Son’), asserting that the Holy Spirit proceeds from the Father and the Son — was added by the Western (Latin) Church but rejected by the Eastern (Greek) Church. This dispute became one of the contributing factors to the Great Schism of 1054 between Roman Catholicism and Eastern Orthodoxy.

The Ecumenical Councils and Creeds