Today we remember the first Ecumenical Council of the Church. It is now famous for its Christian statement of belief that is widely used in liturgy. What is an ecumenical council and what authority does it have? Why was this council called and what was Arianism? Why does it matter to Christians how Jesus relates to the rest of the Trinity?
An Ecumenical council is a universal meeting of church leaders, in contrast to a local council. Because of its universal nature it has a particular authority and can agree on decrees that concern faith or morals, to which the whole Church must adhere. Such decrees are often labelled as 'Canons', often as a response to what is perceived as wide spread heresy, or false teaching. These canons often have an attached anathema, a penalty of excommunication, against those who refuse to believe the teaching. The Catholic Church continues to hold general councils of the bishops in full communion with the Pope, defining them as ecumenical. In all, they would call twenty-one councils as being ecumenical. Other Churches would consider earlier councils as ecumenical but this widespread recognition would stop after divisive events which lead to large sections of the Christian Community breaking communion, such as the Great Schism of the Eleventh Century or the Reformations of the 16th Century.
There is a doctrine of the infallibility of ecumenical councils associated with this ecclesiology, different versions of which are understood by the Eastern Orthodox and the Roman Catholic church. However, the Catholic Church holds that solemn definitions of ecumenical councils meet the conditions of infallibility only when approved by the Pope, while the Eastern Orthodox Church holds that an ecumenical council is itself infallible when pronouncing on a specific matter. Protestant churches would generally view ecumenical councils as fallible human institutions that have no more than a derived authority. This would depend on the extent that they are understood to have correctly expound Scripture. Mainstream protestants, generally consider the first four councils as authoritative in regard to their dogmatic decisions.
This First Council of Nicaea clarified four important matters of belief and authority. Firstly, it repudiated the Christology heresy of Arianism, that is the teaching that the Son of God, Jesus Christ is not co-eternal with God the Father and is therefore distinct from and subordinated to the Father. Following on from this, secondly it declared that Christ is "homoousios with the Father" (of the same substance as the Father), and adopted the original Nicene Creed which is still recited publicly on a Sunday in many churches. Thirdly they fixed the date of Easter and finally recognised the authority of the sees of Rome, Alexandria and Antioch outside their own civil provinces and granted the see of Jerusalem a position of honour. The creed in common usage now is sometimes called more accurately the "Niceno-Constantinopolitan Creed" as it was slightly modified at the Second Ecumenical Council held 56 years later in Constantinople in 381. It is the only authoritative ecumenical statement of the Christian faith accepted by the Catholic Church, the Orthodox Church, and much of Protestantism including the Anglican communion. Other widely used creeds such as the Apostles' and Athanasian creeds are not as widely accepted.
In the recently revised English Translation of the Mass, the English-speaking Catholic Community reverted to Credo in Latin "I believe",in place of the plural form ("we believe") used by the council. This brings them in line with the Orthodox Church's use of the text. The text ends with anathemas against Arian propositions, and these are preceded by the words "We believe in the Holy Spirit". the Lord and Giver of life, who proceeds from the Father, who with the Father and the Son together is worshiped and glorified. In the late 6th century, some Latin-speaking churches added the words "and from the Son" (Filioque) to the description of the procession of the Holy Spirit, in what many Eastern Orthodox Christians have at a later stage argued is a violation since the words were not included in the text by either the Council of Nicaea or that of Constantinople. It eventually became one of the main causes for the East-West Schism in 1054, and the failures of the repeated union attempts. The Vatican stated in 1995 that the word Filioque is not heretical when associated with the Latin verb procedo and the related word processio, which required the affirmation of the Filioque to avoid the heresy of Arianism.