What is the purpose of the other appointed fasts?

The fasts of the Nativity and of the Dormition are preparatory exercises of abstinence, the better to honor the ensuing feasts of the Nativity of the Lord and of the falling asleep of the Mother of God; the fast of the holy Apostles serves the like purpose, and also imitates the Apostles themselves, who fasted to prepare for the work of preaching the Gospel: “after fasting and praying, they laid their hands on Barnabas and Saul and sent them on their way” (Act 13:3).