The Jesus Prayer, and the warmth which accompanies it
To pray is to stand spiritually before God in our heart in glorification, thanksgiving, supplication, and contrite penitence. Everything must be spiritual. The root of all prayer is devout fear of God; from this comes belief about God and faith in Him, submission of oneself to God, hope in God, and cleaving to Him with the feeling of love, in oblivion of all created things. When prayer is powerful, all these spiritual feelings and movements are present in the heart with corresponding vigour.
How does the Jesus Prayer help us in this?
Through the feeling of warmth which develops in and around the heart as the effect of this Prayer.
The habit of prayer is not formed suddenly, but requires long work and toil.
The Jesus Prayer, and the warmth which accompanies it, helps better than anything else in the formation of the habit of prayer.
Note that these are the means, and not the deed itself.
It is possible for both the Jesus Prayer and the feeling of warmth to be present without real prayer. This does indeed happen, however strange it may seem.
When we pray we must stand in our mind before God, and think of Him alone. Yet various thoughts keep jostling in the mind, and draw it away from God. In order to teach the mind to rest on one thing, the Holy Fathers used short prayers and acquired the habit of reciting them unceasingly. This unceasing repetition of a short prayer kept the mind on the thought of God and dispersed all irrelevant thoughts. They adopted various short prayers, but it is the Jesus Prayer which has become particularly established among us and is most generally employed; ‘Lord Jesus Christ, Son of God, have mercy upon me, a sinner!’
So this is what the Jesus prayer is. It is one among various short prayers, oral like all others. Its purpose is to keep the mind on the single thought of God.
Whoever has formed the habit of this Prayer and uses it properly, really does remember God incessantly.
Since the remembrance of god in a sincerely believing heart is naturally accompanied by a sense of piety, hope, thanksgiving, devotion to God’s will, and by other spiritual feelings, the Jesus Prayer, which produces and preserves this remembrance of God, is called spiritual prayer. It is rightly so called only when it is accompanied by these spiritual feelings. But when not accompanied by them it remains oral like any other prayer of the same type.
This is how one should think of the Jesus Prayer. Now what is the meaning of this warmth which accompanies the practice of the Prayer?
In order to keep the mind on one thing by the use of short prayer, it is necessary to preserve attention and so lead it into the heart: for so long as the mind remains in the head, where thoughts jostle one another, it has not time to concentrate on one thing. But when attention descends into the heart, it attracts all the powers of the soul and body into one point there. This concentration of all human life in one place is immediately reflected in the heart by a special sensation that is the beginning of future warmth. This sensation, faint at the beginning, becomes gradually stronger, firmer, deeper. At first only tepid, it grows into warm feeling and concentrates the attention upon itself. And so it comes about that, whereas in the initial stages the attention is kept in the heart by effort of will, in due course this attention, by its own vigour, gives birth to warmth in the heart. This warmth then holds the attention without special effort. From this, the two go on supporting one another, and must remain inseparable; because dispersion of attention cools the warmth, and diminishing warmth weakens attention.
From this there follows a rule of the spiritual life: if you keep the heart alive towards God, you will always be in remembrance of God. This rule is laid down by St. John of the Ladder.
The question now arises whether this warmth is spiritual. No, it is not spiritual. It is ordinary physical warmth. But since it keeps attention of the mind in the heart, and thus helps the development there of the spiritual movements described earlier, it is called spiritual—provided however, that it is not accompanied by sensual pleasure, however slight, but keeps the soul and body in sober mood.
From this it follows that when the warmth accompanying the Jesus Prayer does not include spiritual feelings, it should not be called spiritual, but simply warm-blooded. There is nothing itself bad about this warm-blooded feeling, unless it is connected with sensual pleasure, however slight. If it is so connected, it is bad and must be suppressed.
Things begin to go wrong when the warmth moves about in parts of the body lower than the heart. And matters become still worse when, in enjoyment of this warmth, we imagine it to be all that matters, without bothering about spiritual feelings or even about remembrance of God; and so we set our heart only on having this warmth. This wrong course is occasionally possible, though not for all people, nor at all times. It must be noticed and corrected, for otherwise only physical warmth will remain, and we must not consider this warmth as spiritual or due to grace. This warmth is spiritual only when it is accompanied by the spiritual impetus of prayer. Anyone who calls it spiritual without this movement is mistaken. And anyone who imagines it to be due to grace is still more in error.
Warmth which is filled with grace is of a special nature and it is only this which is truly spiritual. It is distinct from the warmth of the flesh, and does not produce any noticeable changes in the body, but manifests itself by a subtle feeling of sweetness.
Everyone can easily identify and distinguish spiritual warmth by this particular feeling. Each must do it for himself: this is no business for an outsider.
–Theophan the Recluse
[Igumen Chariton of Valamo, The Art of Prayer (Faber and Faber, 1966), pp 93-95]