The Jesus Prayer is also called the Prayer of the Heart. In Orthodoxy, the mind and heart are to be used as one. St Theophan tells us to keep our "mind in the heart" at all times. Heart means the physical muscle pumping blood, and emotions/feelings, and the innermost core of the person, the spirit. Heart is associated with the physical organ, but not identical with it. Heart means our innermost chamber, our secret dwelling place where God lives. "The heart is but a small vessel; and yet dragons and lions are there, and there poisonous creatures and all the treasures of wickedness; rough, uneven paths are there, and gaping chasms. There likewise is God, there are the angels, the heavenly cities and the treasures of grace; all things are there." So says St. Macarius. Someone said the heart is a dimension of interior consciousness, awareness, where we come in touch with an inner space, a space of no dimensions. This consciousness is timeless, the place where tears reside and deep contact with the present moment abide, and from which restful movement comes. Acting out of our heart means to act lightly, with vigour and enthusiasm. When not in that inner awareness, we are restless, agitated and self-concerned. There is within us a space, a field of the heart, in which we find a Divine Reality, and from which we are called to live. The mind, then, is to descend into that inner sanctuary, by means of the Jesus Prayer or wordless contemplation, and to stay there throughout our active day, and evening. We descend with our mind into our heart, and we live there. The heart is Christ's palace. There, Christ the King comes to take His rest.There is that in the Jesus Prayer that lives in the very brokenness of the human heart. When we pray the Prayer, we are not trying to pray as we would like to be, or as we think someone else might think we ought to be, but as we actually are. If our hearts are full of pain, full of the darkness of temptation or of betrayal, distracted, covetous, or grieving, then that is how we will pray. This is one reason why, incidentally, I always use the form the the Prayer that includes the final phrase "a sinner" - for that is who I am, and the two words include all these emotions, and more. For in acknowledging myself a sinner, I am acknowledging my identity, my solidarity even, with the rest of humanity, fallen as we are, and even with the rest of creation in the mysterious brokenness it shares with us, in the pain of the mouse in the owl's claws, of the grasslands in drought. And so the Prayer becomes a prayer for all who suffer, human or otherwise; a true intercession, a stepping into the mercy of God on behalf of all that is.
Albert S Rossi, Saying the Jesus Prayer
Perhaps this intercessory dimension of the Jesus Prayer may help to explain the difficulty sometimes encountered in its practice. I don't mean the ordinary kind of distraction, shopping lists or fantasies drifting across the field of prayer, but a real and painful struggle that sometimes makes it all but impossible inwardly to pronounce even the words of the Prayer. This kind of struggle seems not to be written of much in recent literature, though it crops up often enough in the writings of St Macarius (300-391AD) and others of his period. In his now out of print booklet Praying the Jesus Prayer (Marshall Pickering 1988) Brother Ramon SSF, though, wrote,
The Christian is well aware of the fact that the world is also evil. There is a falseness and alienation which has distracted and infected the world, and men and women of prayer, by the power of the Name of Jesus, stand against the cosmic darkness, and enter into conflict with dark powers. 'For we are not contending against flesh and blood, but against the principalities, against the powers, against the world rulers of this present darkness, against the spiritual hosts of wickedness in the heavenly places.' The power of the Jesus Prayer is the armour against the wiles of the devil, taking heed of the apostle's word: 'Pray at all times in the Spirit, with all prayer and supplication.' [Ephesians 6.12,18 RSV]But I don't want to make too much of this aspect of the use of the Prayer. It does happen, and so it is as well to be aware of it, but it is not what the Prayer is all about. We are praying for the mercy of God in Christ, and it is only through the cross of Christ that God's mercy can heal us, and the wounds for which we pray. "The light shines in the darkness, and the darkness has not overcome it." (John 1.5 NIV) In the repetition of the Jesus Prayer, we are ourselves walking the way of the cross, playing our own small part in its mercy.