Today, 1 September, marks the beginning of a new ecclesiastical year in the Eastern Catholic churches: a new cycle of Gospel readings, feasts, and saints' days. Roman Catholics and other western Christians who are used to the liturgical year beginning on the first day of the Advent season, in late November or early December, may wonder why this is so.
In the Eastern churches, this day is also known as the beginning of the new indiction, which is a clue to the origin of this practice. In the later Roman empire, an indiction was a period of years originally used for taxation and fiscal administrative purposes. This practice dates to the early 3rd Century AD, and under the emperor Constantine was standardised as a period of 15 years, beginning in AD 313, around the same time that the emperor granted rights to Christians and set the groundwork for Christianity to become the official religion of the Empire. The term indiction came refer to a year within a particular indiction era.
Initially, the date of the beginning of a new indiction year was set as 23 September, an imperial holiday marking the birthday of the first emperor, Augustus. This was later changed to 1 September, to instead associate the date with what tradition held was the beginning of Christ's public ministry. The synchronising of ecclesiastical and imperial indiction years speaks to the role of the Church within the later Roman state, as instituted by Constantine and his successors. The Eastern churches, as inheritors of the Roman/Byzantine tradition, maintain 1 September as the beginning of the new ecclesiastical indiction.
Holy tradition associates 1 September with the beginning of Christ's public ministry, when he entered the synagogue in his home town of Nazareth, as recorded in Luke 4:16–22, and read aloud the words of the prophet Isaiah:
A Spirit of the Lord is upon me; hence he has anointed me to announce good tidings to the destitute, he has sent me out to proclaim release to captives and sight to the blind, to send the downtrodden forth in liberty, to proclaim the Lord's acceptable year.