The ancient prayer known as the Jesus Prayer runs, with some variations, as follows:
"Lord Jesus Christ, Son of God, have mercy on me, a sinner."
The Jesus Prayer is more popular in the East than in the West. And it is more common in the mystical strands of Orthodoxy than in the Eastern Church proper. Like other mystic prayers, the object of the Jesus Prayer is to pray it continually, until it becomes one's breath and a fiber of one's being. It almost certainly dates back to the Desert Fathers of the 5th Century, and its practice is now centered in the Monastic state of Mount Athos.
Early practicioners of the prayer associated it with purification of the soul and a sense of inner peace. It takes its place alongside the meditative chanting of Buddhism, Hinduism, and Islam. It has been recommended by Saint John Cassian and Saint John Climacus, and forms the core of the anonymous spiritual classic "The Way of the Pilgrim."
Theologically, the prayer holds two components, the first acknowledging the divinity of Christ, the second recognizing one's own sinfulness. Together, these parts plead mercy. The Jesus Prayer supports a way of prayer called Hesychiasm, or keeping stillness. In Hesychiastic prayer, one invokes the power of the name of God or Christ rather than imaging their presence, as is common in Western contemplation.
This makes the Jesus Prayer more in keeping with apophatic or negative theology, and less in accordance with the ontological theologies of the West. It is more concerned with God's transformative energies than specific doctrinal formulations. Similarly, it confesses no specific sin as in the theological courtrooms of the West, but confesses sin as illness in the spiritual houses of the East.
As a hesychastic practice, the Jesus Prayer demands setting the mind apart from rational activities and ignoring the physical senses for the experiential knowledge of God. It stands along with the regular expected actions of the believer (prayer, almsgiving, repentance, fasting etc.) as the response of the Orthodox Tradition to Pau's challenge to "pray without ceasing"