Great Lent is the greatest fasting period in the church year in Eastern Christianity, which prepares Christians for the greatest feast of the church year, Easter (or "Holy Pasch"). Although it is in many ways similar to Lent in Western Christianity, there are important differences in the timing of Lent (besides calculating the date of Easter), the underlying theology, and how it is practiced, both liturgically in the church and personally.

Before Great Lent itself, there is a Pre-Lent season to prepare for Lent. (Ash Wednesday is not observed in Eastern Christianity.) On three successive Sundays, they remember Zaccheus, the Publican and Pharisee, and the Prodigal Son. Next comes Meatfare Sunday, the last day to eat meat before Great Lent and remembering the Last Judgment. It is followed by Cheesefare Sunday, the last day to eat dairy products before Great Lent; this is also Forgiveness Sunday, when Eastern Christians identify with Adam and Eve, and forgive each other in order to obtain forgiveness from God, typically in a Forgiveness Vespers service that Sunday evening.

This is followed by Great Lent itself, which includes five Sundays, each with a specific reminder or commemoration. During this time, there is a liturgical fast during the week, when the eucharistic Divine Liturgy is not celebrated; the Liturgy of the Pre-sanctified Gifts may however be celebrated on Wednesdays and Fridays, in which believers partake of the Eucharist from the previous Sunday. On Saturday and Sunday, the normal Divine Liturgy may be celebrated, but the ascetical fast from certain foods continues unbroken until Easter. This liturgy of the Pre-sanctified Gifts is one of Eastern Orthodoxy's liturgical distinctives.

Great Lent officially concludes with Lazarus Saturday, the day before Palm Sunday. However, fasting continues for the following week, known as Passion Week or Holy Week, up until Pascha or Easter Sunday. Like Western Lent, Great Lent itself lasts for forty days, although they are counted slightly differently.

One prayer that is said often, accompanied by great prostrations, is the Prayer of St. Ephraim the Syrian. One translation of it is:

O Lord and Master of my life, do not give me the spirit of laziness, meddling, self-importance and idle talk.
Instead, grace me, Your servant, with the spirit of modesty, humility, patience, and love.
Indeed, my Lord and King, grant that I may see my own faults, and not condemn my brothers and sisters, for You are blessed unto ages of ages. Amen.

One book commonly read during Great Lent, particularly by monastics, is The Ladder of Divine Ascent, which was written in about the seventh century by St. John of the Ladder at St. Catherine's monastery on Mt. Sinai.

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