From Bishop Kallistos Ware's Inner Kingdom pg 75
Praying without Ceasing:
The Literal Interpretation
"Pray without ceasing" (I Thess 5:17): the short but emphatic command of St Paul to the Thessalonians has exercised a decisive inflence upon the spirit of Eastern Orthodox monasticism. (1)
1) The Best discussion of the subject, to which I am much indebted, is still Irenee Hausherr, Noms du Christ et voies, Orientalia Christiana Analecta 157 (Rome: Pont. Institutum Orientalium Studiorum, 1960), especially 123-157; English Translation, The Name of Jesus, Cistercian Studies Series 44 (Kalamazoo, MIL Cistercian Publications, 1978), especially 119-89. For a briefer treatment, see Igumen Chariton, The Art of Prayer, especially 80-88.
The Name of Jesus by Irenee Hausherr
The Art of Prayer by Igumen Chariton