Developing the heart means developing within it a taste for things holy, divine, and spiritual, so that when it finds itself amidst such things it would feel as though it were in its element. Finding them sweet and blessed, it would be indifferent to all else, with no taste for anything else; and even more—it would find anything else revolting. All of man's spiritual activity centers in the heart. The truths are impressed in it, and good dispositions are rooted into it. But its main work is developing a taste for the spiritual, as we have shown. When the mind sees the whole spiritual world and its different components, various good beginnings ripen in the will. The heart, under their influence, should taste sweetness in all of this and radiate warmth. This delight in the spiritual is the first sign of the regeneration of a soul deadened by sin. Therefore the heart's development is a very important point even in the early stages.
The work directed at it is all of our Church services in all forms—common and personal, at home and in church—and it is mainly achieved through the spirit of prayer moving within it.
Church services, that is, all the daily services, together with the entire arrangement of the church's icons, candles, censing, singing, chanting, movements of the clergy, as well as the services for various needs;  then services in the home, also using ecclesiastical objects such as sanctified icons, holy oil, candles, holy water, the Cross, and incense—all of these holy things together acting upon all the senses—sight, hearing, smell, touch, and taste—are the cloths that wipe clean the senses of a deadened soul. They are the strongest and the only reliable way to do it. The soul becomes deadened by the spirit of the world, and possessed by sin that lives in the world. The entire structure of our Church services, with their tone, meaning, power of faith, and especially the grace concealed within them, have an invincible power to drive away the spirit of the world. In freeing the soul from the world's onerous influence, it allows the soul to breathe freely and to taste the sweetness of spiritual freedom. Walking into church we walk into a completely different world, are influenced by it, and change according to it. The same thing happens when we surround ourselves with holy objects. Frequent impressions of the spiritual world more effectively penetrate within and more quickly bring about a transformation of the heart. Thus:
1) It is necessary to establish a pattern of going to church as often as possible, usually to Matins, Liturgy and Vespers. Have a longing for this, and go there at the first opportunity—at least once a day—and if you can, stay without leaving. Our church is heaven on earth. Hasten to church with the faith that it is a place where God dwells, where He Himself promised to quickly hear prayers. Standing in church, be as if you are standing before God in fear and reverence, which you express through patient standing, prostrations, and attention to the services without wandering thoughts, relaxation or crudeness.
2) You must not forget other services—personal services, be they in church or at home. Neither must you neglect your home prayers with all their churchly tone. You should remember that home services are only a supplement to church services and not a replacement. The Apostle, commanding us not to deprive ourselves of a synaxis, informed us that all the power of services belong to common worship.
3) You must observe all Church solemnities, rituals, customs, and rubrics, and cover yourself with them in all their forms, so that you would always abide in a particular atmosphere. This is easy to do. Such is the nature of our Church. Only accept it with faith.
But what gives the most power to church services is a prayerful spirit. Prayer is an all-encompassing obligation, as well as an all-effective means. Through it the truths of the faith are also impressed in the mind and good morals into the will. But most of all it enlivens the heart in its feelings. The first two go well only when this one thing [prayer] is present. Therefore prayer should begin to be developed before anything else, and continued steadily and tirelessly until the Lord grants prayer to the one who prays.
The beginnings of prayer are applied at conversion itself, for prayer is the yearning of the mind and heart towards God, which is what happens at conversion. But inattentiveness or inability can extinguish this spark. Then right away you should begin the form of activity that we have already discussed, with the aim of kindling a prayerful spirit. Besides conducting services and participating in them, as we have described, the closest thing related to this is personal prayer, wherever and however it is performed. There is only one rule for this—accustom yourself to praying. For this you must:
1) Choose a rule of prayer—evening, morning and daily prayers.
2) Start with a short rule at first, so that your unaccustomed spirit will nor form an aversion to this labor.
3) Pray always with fear, diligence and all attention.
4) This requires: standing, prostrations, kneeling, making the sign of the Cross, reading, and at times singing.
5) The more often you do such prayer the better. Some people pray a little every hour.
6) The prayers you should read are written in the prayer book. But it is good to get used to one or another, so that the spirit would ignite each time you begin it.
7) The rule of prayer is simple: standing at prayer, with fear and trembling say it as if you were speaking into God's ear, accompanying it with the sign of the Cross, prostrations and failing down, corresponding to the movement of the spirit.
8) Once you have chosen a rule you should always fulfill it, but this does not prevent you from adding something according to the heart's desire.
9) Reading and singing out loud, in a whisper, or silently is all the same, for the Lord is near. But sometimes it is better to pray one way, other times another.
10) You should firmly keep in mind the limits of your prayers. It is a good prayer that ends with your falling down before God with the feeling that Thou Who knowest the hearts, save me.
11) There are stages of prayer. The first stage is bodily prayer, with reading, standing and prostrations. If the attention wanders, the heart does not feel, and there is no eagerness; this means there is no patience, toil or swear. Regardless of this, set your limits and pray. This is active prayer. The second stage is attentive prayer: the mind gets used to collecting itself at the hour of prayer, and says all with awareness, without being stolen away. The attention blends with the written words and repeats them as its own. The third stage is prayer of the feelings—the attention warms the heart, and what was thought with attention becomes feeling in the heart. In the mind was a compunctionate word, in the heart it is compunction; in the mind-forgiveness, in the heart—a feeling of its necessity and importance. Whoever has passed on to feeling prays without words, for God is a God of the heart. This, therefore, is the summit of prayer's development: while standing in prayer, to from feeling to feeling. Reading may stop at this, just as may thought; then there is only abiding in feeling with the known signs of prayer. Such prayer comes very little at first. The prayerful feeling comes over you in church or at home.... This is the common advice of the saints—do not let this leave your attention: when the feeling is present, cease all other activity and stand in it. St. John of the Ladder says: "An angel is praying with you." Attention to this manifestation of prayer ripens the development of prayer, and inattention decimates both the development and the prayer.
12) However, no matter how perfect one has become in prayer, the prayer rule should never be abandoned but should always be read as prescribed and always begun with active prayer. Mental prayer should come with it, and then prayer of the heart. Without the rule, prayer of the heart is lost, and the person will think that he is praying, but in fact he is not.
13) When the prayerful feeling ascends to ceaselessness, then spiritual prayer begins—a gift of the Spirit of God which prays for us. This is the last stage of attainable prayer. But it is said that there is also prayer that is incomprehensible to the mind, or surpasses the limits of awareness (as described by St. Isaac the Syrian).
14) The easiest means for ascending to ceaseless prayer is the habit of doing the Jesus Prayer and rooting it in yourself. The most experienced men of spiritual life who were enlightened by God found this to be the one simple and all-effective means for confirming the spirit in all spiritual activities, as well as in all spiritual ascetic life; and they left detailed guidelines for it in their instructions.
By laboring in asceticism we seek purification of the heart and renewal of the spirit. There are two ways to find this: the first is the way of activity, that is, performing those ascetic labors that we have previously outlined; and the second is that of the mind-turning the mind to God. In the first way the soul is purified and receives God, in the second God burns away all impurity and comes to abide in the purified soul. Considering the latter as belonging to the Jesus Prayer alone, St. Gregory the Sinaite says: "We acquire God by either activity, labor, or the artful calling on the Name of Jesus." He then supposes that the first way is longer than the second; the second is quicker and more effective. Others after him have given first place to the Jesus Prayer among podvigs. It illuminates, strengthens, enlivens, conquers all enemies visible and invisible, and leads us to God. That is how powerful and effective it is! The name of the Lord Jesus is the treasury of blessings, strength and life in the spirit.
From this it is evident that any penitent, or anyone beginning to seek the Lord, can and should be taught complete instructions in doing the Jesus Prayer. From there he can be brought into all other practices, because through this he will become strong more quickly, ripen sooner spiritually and enter the interior world. Not knowing this, other people, or at least a large part of them, stop with bodily activities and those of the soul, and waste nearly all their labor and time.
This activity is called an "art." It is very simple. Standing with awareness and attention in the heart, pronounce ceaselessly: "Lord Jesus Christ, Son of God, have mercy on me," without picturing any sort of image or face, but with faith that the Lord will see you and attend to you.
In order to become strong in this, you should assign a time in the morning or the evening—fifteen minutes, a half hour, or more—however much you can, just for saying this prayer. It should be after morning or evening prayers, standing or sitting. This will place the beginnings of a habitual practice.
Then during the day, force yourself minute-by-minute to say it, no matter what you are doing.
It will become more and more habitual, and then it will start working as if by itself during any work or occupation. The more resolutely you take it up, the faster you will progress.
Your awareness should be kept unfailingly in the heart, and during the practice your breath should lighten as a result of the tension with which you practice it. But the most important condition is faith that God is near and hears us. Say the prayer into God's ear.
This habitual practice will draw warmth into the spirit, later enlightenment, then ecstasy. But acquiring all of this sometimes takes years.
At first this prayer is only active prayer, just like any other activity. Then it becomes mental prayer, and finally it takes root in the heart.
Some have gone astray from the right path through this prayer. Therefore it should be learned from someone who knows it. Deception comes mostly from placing the attention on the head rather than the chest.
Whoever has the attention centered in the heart is safe. Even safer is the one who falls down before God every hour in contrition, with the prayer that he be delivered from deception.
The Holy Fathers gave detailed instructions on this activity. Therefore, whoever takes up this work should read these instructions and throw out all else. The best instructions are by St. Hesychius, St. Gregory the Sinaite, St. Philotheus of Sinai, St. Theoleptus, St. Symeon the New Theologian, St. Nilus of Sora, Hieromonk Dorotheus, in the prologue to Elder Barsanuphius, and in the life of St. Paisius.
Whoever becomes practiced in this, having gone through everything set forth above, is a practitioner of Christian life. He will quickly ripen in his purification and in Christian perfection, and will acquire his desired peace in being with God.
This is the activity for the powers of the soul, which are adaptable to the movement of the spirit. Here we see how every one of them is adapted to the life of the spirit, or to spiritual feeling. But they also lead to the fortification of the primary conditions for being within, namely: mental activity—the concentration of attention; activity of the will—vigilance; activity of the heart—soberness. Prayer covers them all and encompasses them all. Even the production of it is nothing other than the interior work we have previously described.
All of these activities are assigned for the development of the powers of the soul in the spirit of a new life. This is the same as infusing the soul with spirit, or elevating it to the spirit and blending with it. In fallenness they are united to a contrary purpose. At conversion the spirit is renewed, but in the soul there still remains a cruet streak of unsubmissiveness and an aversion to the spirit and everything spiritual. These activities, penetrated with spiritual elements, cause the soul to grow into the spirit and blend with it. It is clear from this how essential these activities are and what a disservice those people do to themselves who abandon them. They themselves are the reason that their labors are fruitless. They sweat but see no fruit; they soon grow cold, and then everything comes to an end.
But we must remember that all the fruits of these labors come from the spirit of zeal and quest. It conducts the renewing power of grace through these activities and brings down life into the soul. Without it, all these activities are empty, cold, lifeless, and dry. Reading, prostrations, services and everything else are unfruitful when there is no inner spirit. They can teach vainglory and pharisaism, which become its sole support. This is why someone who has no spirit falls away when he meets with any opposition. Why, they themselves are a torture. For the spirit transfers power to the soul, which makes the soul so well disposed to these activities that it can not get enough of them and wants to have recourse to them always.
Thus it is extremely necessary when doing these activities to always bear in mind that the spirit of life must burn within, and we must in humility and pain of heart fall down before God our Savior. This state is fed and preserved best of all by prayer and prayerful activity. We must watch that we not stop with the activities alone just because they also nourish the soul. This might cause us to remain with them in soul at the cost of the spirit. This happens perhaps most often with reading, and generally any study and integration of the truth.
From The Path to Salvation, trans. Fr. Seraphim Rose and the Saint Herman of Alaska Brotherhood (Platina, 1996)