"In the desert, (the Desert Fathers and Mothers) ...experimented with
different forms of constant prayer. They recognized that the task was to discipline the wandering mind and focus it on something spiritually healthful, so they memorized the Scriptures (the Psalms in particular) and quietly murmured the verses to themselves throughout the day.
Great depths could be found in a single line. Abba Pambo (AD 303-75) could not read, so he asked another desert dweller to teach him a psalm. When he heard the first words of Psalm 39, "I will guard my ways, that I may not sin with my tongue," he asked the other monk to stop and then meditated on that verse alone - for nineteen years. (Asked whether he was ready to hear as least the remainder of the verse, he replied that he had not mastered the first part yet.)
Evagrius of Pontus (AD 345 - 99), on the other hand, listed 487 Scriptures each of which was to be memorized and brought forth when needed to combat a specific temptation. St. John Cassian (AD 360-435) recommended the first verse of Psalm 70 as the best all-purpose Scripture for those seeking continual prayer: "Be pleased, O God, to deliver me! O Lord, make haste to help me!"
"The Jesus Prayer" by Frederica Mathewes-Green