Oxford Dictionary of Christian Church History on Hesychasm ("Quiet"), a fourteenth-century Mount Athos mystical system: Its chief tenet was that by perfect quiet of body and mind man is able to arrive at vision of the "Uncreated Light of the Godhead." The result of these practices was ineffable joy and seeing the Light, which surrounded Our Lord on Mount Tabor. It was held that this Light was not God's essence, which is unapproachable, but his Energy which can be perceived by the senses, and that it was this Light, and not, as Western theologians hold, God's Essence, which is the object of the Beatific Vision. Philotheus Kokkinus in his contribution to the anthology called Hagioritic Tome, written at Mount Athos about 1339, states that the Mount Athos doctrine of Divine Light was revealed experientially to the contemplatives who lived there.
Easier methods, therefore more mechanical, to procure this vision of Divine Light, included: (a) breathing exercises, (b) pressing chin against the chest, (c) indefinite repetition of the ejaculation "Lord Jesus Christ have mercy on me." Hesychast theology conceives of God as a compound of essence and activity, whereas Western theology denies the possibility of an uncreated light that was not God's essence, on the grant that any distinction would destroy His unity and simplicity.
-- Notebooks Category 22: Inspiration and the Overself > Chapter 4 : Introduction To Mystical Glimpses > # 199
