The First Ecumenical Council (Nicaea, 325) decreed that the Church year should begin on September 1. The month of September was, for the Hebrews, the beginning of the civil year (Exodus 23:16), the month of gathering the harvest and of the offering of thanks to God. It was on this feast that the Lord Jesus entered the synagogue in Nazareth (Luke 4:16-21), opened the book of the Prophet Isaiah and read the words: The Spirit of the Lord God is upon Me; because the Lord hath anointed Me to preach good tidings unto the meek; He hath sent Me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to them that are bound; to proclaim the acceptable year of the Lord, and the day of vengeance of our God; to comfort all that mourn (Isaiah 61:1-2). The month of September is also important in the history of Christianity, because Emperor Constantine the Great was victorious over Maxentius, the enemy of the Christian Faith, in September. Following this victory, Constantine granted freedom of confession to the Christian Faith throughout the Roman Empire. For a long time, the civil year in the Christian world followed the Church year, with its beginning on September 1. The civil year was later changed, and its beginning transferred to January 1. This occurred first in Western Europe, and later in Russia, under Peter the Great.

(From  Saint Nikolai Velimirovic, The Prologue of Ohrid – Volume Two.)

SOURCE: https://goarchdiocese.ca/ecclesiastical-new-year-beginning-of-the-indiction-2/

Ecclesiastical New Year (September 1st)