Great Schema

The degrees of Eastern Orthodox monasticism are the stages an Eastern Orthodox monk or nun passes through in their religious vocation.

In the Eastern Orthodox Church, the process of becoming a monk or nun (female ascetics in the East are called monks, nun is a Western tradition) is intentionally slow, as the monastic vows taken are considered to entail a lifelong commitment to God, and are not to be entered into lightly. After completing the novitiate, there are three degrees of or steps in conferring the monastic habit.

Unlike in Western Christianity, where individual religious orders and societies arose, each with its own profession rites, in the Eastern Orthodox Church, there is only one type of monasticism. The profession of monastics is known as Tonsure (referring to the ritual cutting of the monastic's hair which takes place during the service) and was, at one time, considered to be a Sacred Mystery (Sacrament). The Rite of Tonsure is printed in the Euchologion (Church Slavonic: Trebnik), the same book as the other Sacred Mysteries and services performed according to need, e.g., funerals, blessings, exorcisms, etc.

The monastic habit is the same throughout the Eastern Church (with certain slight regional variations), and it is the same for both monks and nuns. Each successive grade is given a portion of the habit, the full habit being worn only by those in the highest grade, known for that reason as the "Great Schema", or "Great Habit". One is free to enter any monastery of one's choice; but after being accepted by the abbot (or abbess) and making vows, one may not move from place to place without the blessing of one's ecclesiastical superior.

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Wikipedia