" All these evil things come from within and defile a man." Jesus Christ (Mark 7:23)Maintaing attention is a central part of prayer. Watchfulness is essential. We find our mind is continually influenced by thoughts which pollute our heart. These are not necessarily temptations that come from our external environment but are our reactions to external factors. The thing that we need to gain control over is our inward reactions that generate thoughts and bound up our heart
Saint Theophan says,
"The mind's thoughts are all directed toward this earth, and there is no way to raise them to heaven. Their object is vain, sensual, sinful. You have seen how fog drifts along the valley. This is a precise picture of our thoughts. They all crawl and drift along the earth. In addition to this downward drifting, they constantly seethe, not standing still in a single place; they jostle each other, like a swarm of mosquitoes in the summer. In addition, they are always in motion.
Beneath these there lies the heart. It is from the thoughts that blows are continually struck in the heart and corresponding actions of the heart. from this is joy, anger, envy, fear, hope, pride, despair––they arise in the heart one after the other. There is no stopping them; just as with the thoughts, there is no order whatsoever. The heart continually trembles from the emotions like an aspen leaf."
Our challenge in prayer is to cut off these thoughts.
Elder Nikodim says,
"When the mind is pure, then the heart will be pure. And when the heart is pure, then the mind will also be pure."
When we have mastered this we will find the mind becomes a true partner in our prayer.
Fr. Sophrony says
"The mind becomes all ears and eyes, and sees and hears every extrinsic thought approaching from without, before it can invade the heart. Praying the while, the mind not only refuses to admit extraneious thoughts into the heart but positively throusts them aside and preserves itself from association with them."
Knowing the interaction between the mind and the heart is an important discovery to make about our inner life.
See Christ the Eternal Tao pp 363-365.
http://agapienxristou.blogspot.ca/2013/03/interaction-of-heart-and-mind-in-prayer.html