Pope Shenouda III
The spiritual prayer is also one of understanding and concentration.
Concentration keeps the thoughts from straying. Understanding also is another factor that enables the mind to concentrate and so does passion. As for the one who prays with no heart, no understanding and no passion, his thoughts will definitely stray in various matters because his heart is not free yet from worldly concerns. He is still attached to them, even during prayer. His prayer would not be pure because it is yet in close contact to the things of the world.
Therefore, when St. John of Assiot was asked, “What is the pure prayer?” He answered, “It is death to the world”, because when the heart dies to worldly matters, it would not ponder on such things during prayer, so his prayer becomes pure without straying.