John Cassian (Ioannes Cassianus)
An exercise long used among Christians for acquiring contemplation, one "available to everyone, whether he be of the clergy or of any secular occupation", involves focusing the mind by constant repetition of a phrase or word. Saint John Cassian recommended use of the phrase "O God, make speed to save me: O Lord, make haste to help me". Another formula for repetition is the name of Jesus. or the Jesus Prayer, which has been called "the mantra of the Orthodox Church", although the term "Jesus Prayer" is not found in the Fathers of the Church. The author of The Cloud of Unknowing recommended use of a monosyllabic word, such as "God" or "Love". This exercise, which for the early Fathers represented just a training for repose, the later Byzantines developed into a spiritual work of its own, attaching to it technical requirements and various stipulations that became a matter of serious theological controversy (see below), and remain of great interest to Byzantine, Russian and other eastern churches.
Hesychasm is a form of constant purposeful prayer or experiential prayer, explicitly referred to as contemplation. It is to focus one's mind on God and pray to God unceasingly.
Under church tradition the practice of Hesychasm has it beginnings in the bible, Matthew 6:6 and the Philokalia. The tradition of contemplation with inner silence or tranquility is shared by all Eastern asceticism having its roots in the Egyptian traditions of monasticism exemplified by such Orthodox monastics as St Anthony of Egypt.
In the early 14th century, Gregory Sinaita learned hesychasm from Arsenius of Crete and spread the doctrine, bringing it to the monks on Mount Athos. The terms Hesychasm and Hesychast were used by the monks on Mount Athos to refer to the practice and to the practitioner of a method of mental ascesis that involves the use of the Jesus Prayer assisted by certain psychophysical techniques. The hesychasts stated that at higher stages of their prayer practice they reached the actual contemplation-union with the Tabor Light, i.e., Uncreated Divine Light or photomos seen by the apostles in the event of the Transfiguration of Christ and Saint Paul while on the road to Damascus.