Origins of the Fast of the Apostles
The Fast of the Holy Apostles is dated back to early years of the church. The first evidence of this fast is found in the writings of St. Athanasius the Great (†373). In his letter to Emperor Constance, he writes: "During the week following Pentecost, the people who observed the fast went out to the cemetery to pray." Some 20 years later, St. Ambrose (†397) writes: "On the days following his ascension into heaven, however, we again fast" (Sermon 61).
The famous pilgrim Egeria mentioned the Apostles' Fast also in her fourth-century-writing which records that "on the day following the feast of Pentecost, a period of fasting began". In the same period, the fourth century, the Apostolic Constitutions prescribes: "After the feast of Pentecost, celebrate one week, then observe a fast, for justice demands rejoicing after the reception of the gifts of God and fasting after the body has been refreshed."
Until the second half of the 3rd century, the Fast of the Holy Apostles was linked to Pentecost and lasted only for one week (Apostolic Constitutions). Later on, after the martyrdom of the apostles Peter and Paul and following the development of the commemoration of their death around the year 258, the Apostles' Fast became linked to the feast of Saints Peter and Paul on June 29. Consequently, it became a fasting period of preparation for the celebration of the feast of the great apostles. St. Symeon of Thessalonica (†1429) explains: "The Fast of the Apostles is justly established in their honor, for through them we have received numerous benefits and for us they are exemplars and teachers of the fast ... For one week after the descent of the Holy Spirit, in accordance with the Apostolic Constitution composed by Clement, we celebrate, and then during the following week, we fast in honor of the Apostles."
Subsequently, the duration of the Fast of the Holy Apostles changed from one week to a variable period depending on the date of the Feast of Pascha (Easter).
Duration of the Fast of the Apostles
The fast of the Holy Apostles starts on the second Monday after Pentecost. The duration of this fast varies, depending on the date of Pascha (Easter). The rule is that the Fast starts on the second Monday after Pentecost and ends on June 29, on the feast of Saints Peter and Paul. According to the new calendar, the Apostles' Fast could last as short as 8 days and as long as 30 days (42 days according to the old calendar).
Fasting Rules of the Fast of the Holy Apostles
The Fast of the Holy Apostles is not as strict as the Fasts of Pascha and the Nativity of Christ; rather it is more lenient in its duration and rules. The current rules of fasting, during the Apostles' Fast, were established first for the monks of the Monastery of the Kiev Caves by Metropolitan George of Kiev (1069-1072). These rules are still practiced today amongst most Orthodox Christians with minor variations, depending on the jurisdiction.
The rules are:
1- Red meat, poultry, and dairy products are not allowed during the entire fasting period in all weekdays.
2- Fish, wine, and oil are allowed on all days except on Wednesdays and Fridays.
The Apostles fast has emerged since the very early days of Christianity. It is honored and preserved in the Church as a part of our Holy Tradition. Like all Fasts in the Orthodox Church, the Holy Apostles' Fast aims to help us put on the "armor of light" to against the attacks of the enemy that may befall during our spiritual journey to become united with God through His grace. No better words may express the importance of fasting in our life like the words of St. Abba Isaac the Syrian who says, "... since fasting is a weapon established by God ...the human race knew no victory before fasting, and the devil was never defeated by our nature as it is: but this weapon has indeed deprived the devil of strength from the outset... As soon as the devil sees someone possessed of this weapon (fasting), fear straightway falls on this adversary and tormentor of ours, who remembers and thinks of his defeat by the Saviour in the wilderness; his strength is at once destroyed and the sight of the weapon given us by our Supreme Leader burns him up. A man armed with the weapon of fasting is always afire with zeal. He who remains therein, keeps his mind steadfast and ready to meet and repel all violent passions."
Courtesy: Antiochian Orthodox Christian Archdiocese here