The institution of the Nativity Fast, as well as other multi-day fast periods, is related to ancient Christian times. Already in the IV century St. Ambrose of Milan, Philistrius and St. Augustine mention the Nativity Fast in their writings. Leo the Great writes about it in the V century. At first the Nativity Fast lasted seven days for Christians, while for others a bit longer. At the Council of 1166, held at the time of Patriarch Luke of Constantinople and Byzantine emperor Manuel a forty-day fast was ordered to be observed by all Christians before the great feast of the Christ’s Nativity.
Antiochian Patriarch Valsamon wrote, that “the very holy patriarch said that even though the days of those fasts (Dormition and Nativity) are not regulated, let us make the effort however to follow the unwritten church tradition and we are obliged to fast…from 15/28 November.” The Nativity Fast is the last multi-day fast of the year. It begins 15/28 November and lasts until 25 December/ 7 January, forty days and for this reason in the Church constitution it is referred to as Quadragesima, like Great Lent. Since the fast from food begins with the feast of St. Philip (14 November according to the Old Style), it is also referred to as Philip’s Fast.
The Nativity Fast is a winter fast and serves for the sanctification of the last part of the year with the mystical renewing of our spiritual unification with God and our preparation for the celebration of Christ’s Nativity. St. Leo the Great writes, “The abidance to abstinence is specified in the four periods, so that during the year we might comprehend that cleansing is constantly necessary and that amid life’s distractions we should always strive by means of fasting and acts of charity to extirpate sin, sin which is multiplied in our transitory flesh and in our impure desires.”
According to Leo the Great, the Nativity Fast is a sacrifice to God in return for the gathered harvest. The holy Saint says, “Just as the Lord has generously granted us abundance of earthly fruits, so too should we, during the time of this Fast, be generous to the poor.”
According to St. Simeon of Thessaloniki, “the Nativity Forty-day Fast represents the fast undertaken by Moses, who, having fasted for forty days and forty nights, received the Commandments of God, written on stone tablets. And we, fasting for forty days, will reflect upon and receive from the Virgin the living Word – not written upon stone, but born, incarnate, and we will commune of His Divine Body.”
The Nativity Fast was established to allow us through repentance, prayer and fasting to cleanse ourselves before the Nativity of Christ, so that with a clean heart, soul, and body, we might reverently meet the Son of God, Who has come into the world and so that in addition to bringing the usual gifts and sacrifices, we might bring Him our clean hearts and a desire to follow His teachings.