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.