The Great Canon of St. Andrew of Crete is a lengthy penitential canon composed in 7th century, which is performed during the Great Lent. It is divided into four portions, which are read during the Great Compiline on Monday, Tuesday, Wendesday and Thursday of Pure Week. The whole canon is read all over again on Wendesday evening of the fifth week of the Great Lent.
The refrain "Have mercy upon me O Lord, have mercy upon me" accompanies each verse of the Great Canon. Several troparia in honor of St. Andrew, composer of the canon, and to St. Mary of Egypt are also included. The Church of Jerusalem implemented this practice during St. Andrew’s lifetime. When in the year 680 AD, St. Andrew traveled to Constantinople for the 6th Ecumenical Council, he brought with him and made public both his great composition and the life of St. Mary of Egypt, written by his compatriot and teacher, Sophronios, Patriarch of Jerusalem. The Life of St. Mary of Egypt is read together with the Great Canon at Matins on Wednesday of the fifth week of Great Lent.
A basic distinguishing feature of the Great Canon is its extremely broad use of images and subjects taken from Sacred Scripture, both from the Old and New Testaments. As the Canon progresses, the congregation encounters many biblical examples of sin and repentance. The Bible (and therefore, the Canon) speaks of some individuals in a positive light, and about others in a negative one - the penitents are expected to emulate the positive examples of sanctity and repentance, and to learn from and avoid the negative examples of sin, fallen nature and pride. However, one of the most notable aspects of the Canon is that it attempts to potray the Biblical images in a very personal way to every penitant: the Canon is written in such form that the faithful identify themselves with many people and events found in the Old and New Testaments.