Give Evil no Entry

Speaking about the Egyptian desert and why the monastics there were successful at taming their thoughts and the attack of demons,

“But everyone does the work assigned to Him in such a way that, by repeating by heart some psalm or passage of Scripture, he gives no opportunity or time for dangerous schemes or evil designs, or even for idle talk, as both mouth and heart are incessantly taken up with spiritual meditations.”

St. John Cassian, Institutes, Book 2, Chapter 15.