The Jesus Prayer is a constant uninterrupted calling upon the divine name of Jesus with the lips, with the mind, with the heart, while at the same time a mental picture of His constant presence is formed and His Grace dominates, during every job, at all times, in all places, even when we sleep. The prayer is only these few words; Lord Jesus Christ, have mercy on me. One who accustoms himself to this prayer experiences as a result so deep a consolation and so great a need to offer the prayer always that he can no longer live without it, as internally continues to say it in silence such as the prayer becomes a harmonic internal echo of the words. Now do you understand what praying without ceasing is?
From The Way of the Pilgrim
Translated by Dr. Nick Stergiou