The First Council of Nicea took place in 325 in the eastern part of the Roman Empire, from which the later, separate Eastern Roman Empire, also known as the Byzantine Empire, had already gradually begun to emerge. This fact alone indicates that this council for the Byzantine tradition is of significant importance.
First of all, this article will show the First Council of Nicea as the First Universal (Ecumenical) Council, a kind of Proto-Council, which opens a new epoch in the history of the Church since universal councils will decisively influence the development of doctrine. This is very evident especially in Orthodoxy, which identifies this time of universal councils with the First Millennium, recognising only seven ecumenical councils.
The Council of Nicea I laid the foundations for the formation of Christological and Trinitarian dogmas, since it was at this Council that the so-called Nicene Symbol was adopted, in which the doctrine of the Son of God appears extensively expounded, which was later copied in almost unchanged form into the so-called Nicene-Constantinopolitan Symbol.
The second part of the article discusses the disciplinary issues raised at the First Council of Nicea and their validity in the current legislation of the Churches of the Byzantine tradition. In this context, the issue of the attempt to unify the date of celebrating Easter, which is still calculated differently in the Byzantine East than in Western Christianity, was also examined.
The third part of the article is devoted to the significance of the First Council of Nicea in the Byzantine liturgy, especially in the hymns of the 7th Easter Sunday, which recalls the 318 Fathers of the First Council. The influence of the teaching of the First Council of Nicea on the content of the elaborate confession of faith that the bishop–nominate makes just before his chirotony in the Byzantine tradition was also pointed out. Furthermore, it was mentioned how the Byzantine liturgy describes the participation of St Nicholas of Myra at the First Council of Nicea
