On Watchfulness and the Guarding of the Heart.
Because the work is ancient, the original text is in the public domain. However, are usually copyrighted. Here is how to access them legally and safely: filocalia completa pdf
In the digital age, the search for ancient wisdom often begins with a few keystrokes. For Eastern Orthodox Christians, contemplative Catholics, and students of Christian mysticism, few phrases carry as much weight as On Watchfulness and the Guarding of the Heart
: "Lord Jesus Christ, Son of God, have mercy on me," viewed as a method to achieve unceasing prayer. and students of Christian mysticism
: This was the final volume of the English translation project. Because it is newer, it is harder to find as a free, legal PDF.