The Jesus Prayer can be considered practical application of the lesson taught by the parable of the Publican and the Pharisee. The Pharisee demonstrates the improper way to pray by exclaiming: "Thank you Lord that I am not like the Publican", whereas the Publican prays correctly in humility "Lord have mercy on me, the sinner." (Luke 18:10-14.)
In the Eastern tradition the prayer is said or prayed repeatedly. A prayer rope (Russian chotki; Greek komposchini) is often used in addition to the prayer it's self. The cord is usually woolen and tied into many knots. The person saying the prayer says one repetition for each knot.
Orthodox monks often prayed this prayer many hundreds of times each night as part of their private cell vigil. Under the guidance of an Elder (Russian Starets; Greek Gerondas), the monk aims to internalize the prayer so that he is praying unceasingly. Diadochos refers in the Pitfka to the unconcious repetition of the Jesus Prayer, under the influence of the Holy Spirit, even in sleep. This state is regarded as the accomplishment of Saint Paul's exhortation to the Thessalonians to "pray without ceasing". (1 Thessalonians 5:17) The monk's goal is also, in advanced practice, to bring his mind into his heart so as to practice the Jesus Prayer with his mind in his heart.
It can be used as a means of finding contrition or a practice to help facilate humility in the individual. In its more advanced use, the monk aims by the practice of the Jesus Prayer to be moved by Divine grace into a place of contemplation.
In a modern context this continuing repetition is regarded by some as a form of meditation. The prayer functioning as a kind of mantra. However, traditional users of the Jesus Prayer emphasize the invocation of the name of Jesus Christ and the object of the exercises being contemplation on the Triune God rather then simply an emptying the mind.
adapted from several sources.