The fast of Great Lent is a form of abstinence practiced over an extended period of time in which certain foods are abstained from during the Lenten season and/or also food is abstained from for designated periods during the day – for example, in the morning or until after Vespers. Besides the periods of fasting of the various lenten seasons and the usual weekly fasting days in the Orthodox Church there is also a fast done in preparation for receiving Holy Communion. Fr. Alkiviadis Calivas comments:
“In the beginning the Eucharist was celebrated within the context of an evening community meal, referred to as the agape or love feast. By the end of the first or the beginning of the second century, the celebration of the Eucharist was separated from the community meal and transposed to the early morning hours. From that time forward, every Eucharistic celebration is preceded by a fast, called the Eucharistic fast. The Eucharist is Christ himself. It is his sacrificed, risen, and glorified body, which is given to the faithful ‘for the forgiveness of sins and life eternal.’ As such, it is the most precious of gifts, through which the life of God continually becomes the life of those who believe in him, receive him in faith, and abide in him. That is why the Eucharistic fast has become a fixed prerequisite for Holy Communion. It is meant to place the faithful in a state of readiness, vigilance, expectation, and anticipation for an encounter with the living God who calls his people to communion and holiness.
Participation in the Divine Liturgy, therefore, requires prayerful preparation, for we stand on holy ground in the presence of the Triune God (Ex. 3:4-7). Hence, in preparation for this profound experience, we are called to quietness, abstinence, and forebearance, to a quickening of body and soul that we may receive the King of all. Fasted from the night before, as a sign of spiritual vigilance and awareness, we approach the Holy Table ‘with the fear of God, with faith, and with love,’ to receive the Holy Gifts as the first meal of the day and as the essential food of life.” (Essays in Theology and Liturgy, pp 166-167)