...Try taking a walk for ten minutes as you invoke His miracle-working name, and you will see spiritual profit. Begin in a simple, humble manner, "O Lord Jesus Christ, have mercy on me, a sinner."  You may even do this somewhat mechanically, knowing that this tradition has been sanctified by generations of saints, but as you walk and pray, try not to think of anything else. Just walk in the presence of God.

     In these ten minutes you will find that your fevered mind is soothed, that the noisy bazaar of your thoughts has become light, clear, and direct, and that your heart has begun to say other prayers in a manner that satisfies you. You pray, you breathe, you speak to God; you are not just repeating empty words. What does it mean to have your mind in your heart? It means that you are to control your feelings. You are not to admit invaders into your heart, but are to check your heart with your mind, to observe everything that takes place there. To have your mind in your heart is exactly what our Lord prescribes to us in His commandment: When thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father who is in secret.

     If you make progress in this humble prayer, you will begin to understand that this commandment is very complete. Your heart will be filled with a spiritual warmth that embraces the center of your feelings. You will come to understand what attentive prayer is, and that your heart has been created for ceaseless prayer. Ceaseless prayer is not a perpetual repetition of this or that word or phrase. The holy Fathers say that it is the feeling of your heart. Just as you view the objects of this world with open eyes, so your heart, warmed by prayer to God, will partake of the spiritual world. This will be due, not to your piety, but to God's grace. Unceasing prayer may have no words, but you will walk and sleep in the presence of God.

Archpriest Artemy Vladimirov
from Orthodox Christian Parenting, "Guarding Against the Intruders"