The Jesus Prayer has been prayed by faithful Christians for centuries. I learnt about it through reading the book “The Way of a Pilgrim”.
It´s about a pilgrim (unidentified) who, when listening to a sermon, was challenged by the instruction to “pray constantly” (1 Thess 5,17).
But how could he achieve this? He went to a priest who told him to repeat the prayer, “Lord Jesus Christ, Son of God, have mercy on me, a sinner” over and over again.
A long “training” process began and by the end he could even pray the prayer to the beat of his heart. This is why the Jesus Prayer is also called ‘the Prayer of the Heart’.