Let no one think, my Christian brethren, that only clergy and monks have the duty to pray unceasingly and always, and not the laity. No, no; all of us Christians have the duty to always remain in prayer. For consider what His Holiness Philotheus, Patriarch of Constantinople, writes in his Life of St. Gregory of Thessaloniki. This saint had a beloved friend, Job by name, a simple man, but full of virtue, with whom, while conversing one day, the bishop said of prayer that every Christian in general must strive in prayer always, and pray without ceasing, as the Apostle Paul commands all Christians in general: "Pray without ceasing" ( 1 Thessalonians 5:17 ), and as the prophet David says of himself, despite being a king and having care for his entire kingdom: "I have set the Lord before me continually" ( Psalm 16:8 ), that is, I always mentally see the Lord before me in my prayer. And Gregory the Theologian teaches all Christians and tells them that they should remember the name of God in prayer more often than they breathe air.
Saying this and much more to his friend Job, the saint added that, in obedience to the commandments of the saints, we must not only pray always ourselves, but also teach everyone to do the same, everyone in general: monks and laypeople, the wise and the simple, men, women, and children, and encourage them to pray unceasingly. Hearing this, the elder Job thought this was a novelty and began to argue, telling the saint that constant prayer is the work of ascetics and monks only, who live apart from the world and its vanities, and not of laypeople, who have so many cares and concerns. The saint presented new testimonies in support of this truth and new, irrefutable proofs, but the elder Job was not convinced by them either. Then Saint Gregory, avoiding verbosity and argument, fell silent, after which each returned to his cell. While Job was later praying alone in his cell, an angel appeared to him, sent by God, "who desires all to be saved and to come to the knowledge of the truth" ( 1 Tim. 2:4 ). Rebuking him for arguing with Saint Gregory and opposing the obvious matter on which the salvation of Christians depends, the angel declared to him in the person of God that he should first pay attention to himself and beware of saying anything to anyone contrary to this soul-saving matter and resisting the will of God, not even in his mind entertaining any thoughts contrary to this and not allowing himself to reason differently from what Saint Gregory had said. Then the simple elder Job immediately hastened to Saint Gregory, and falling at his feet, asked forgiveness for his contradiction and inquisitiveness, and revealed to him all that the Angel of the Lord had said.
You see now, my brethren, how obligated all Christians, from the least to the greatest, are to pray always with the mental prayer: "Lord Jesus Christ, have mercy on me!" so that their minds and hearts may be trained to continually utter these sacred words. See for yourself how much this pleases God and how great a blessing results from it, how He, in His boundless love for mankind, sent a heavenly angel to declare to us, so that no one should have any further doubts about this. But what do the laity say? We are burdened with the affairs and cares of this world: how is it possible for us to pray unceasingly? I answer them: God has not commanded us anything impossible, but only what we can do. Therefore, even this can be fulfilled by anyone who zealously seeks the salvation of their soul. For if this were impossible, then it would be impossible for all the laity in general, and then there would not be found so many and so many persons who in the world have perfected this work of unceasing prayer, as follows, of which let the representative of many other such persons be the father of Saint Gregory of Thessaloniki, that wonderful Constantine, who, despite the fact that he moved in the circle of court life, was called the father and teacher of Emperor Andronicus, and was occupied every day with state affairs, in addition to his domestic affairs, as one who had great property and many slaves - a wife and children - despite all this, he was so not excommunicated from God, and so attached to the mental unceasing prayer, that he often forgot that the Emperor and the court nobles spoke to him about royal affairs, and often asked about the same thing two or more times; The other nobles, not knowing the reason, were perplexed and reproached him for forgetting the matter so quickly and burdening the Tsar with repeated questions. But the Tsar, knowing the reason, defended him and said: "Constantine has his own thoughts, which sometimes prevent him from paying full attention to our affairs."
There were many others like them, who, while living in the world, were entirely devoted to mental prayer, as historical records confirm. "And so, my Christian brethren, I implore you, and I, along with St. Chrysostom, for the sake of the salvation of your souls, do not neglect the practice of such prayer. Imitate those I have mentioned and, as much as possible, follow them. At first, this may seem very difficult, but rest assured, as if from the Almighty God, that this very name of our Lord Jesus Christ, constantly invoked by you, will help you overcome all difficulties. And with time, you will become accustomed to this practice and taste how sweet the name of the Lord is."
Then you will know by experience that this task is not only not impossible or difficult, but also possible and easy. This is why Saint Paul, who knew better than we do the great benefit this prayer would bring, commanded us to pray without ceasing. He would not have obliged us to this if it were extremely difficult and impossible, knowing beforehand that in such a case, unable to fulfill it, we would inevitably be disobedient to him and transgressors of his commandment, and thus worthy of condemnation and punishment. But this could not have been the Apostle's intention.
Moreover, consider the method of prayer, how it is possible to pray without ceasing—namely, to pray with the mind. And we can always do this if we wish. For when we sit at our needlework, and when we walk, and when we eat, and when we drink, we can always pray with the mind and offer mental prayer, pleasing to God, true prayer. Let us work with the body, and pray with the soul. Let our outer man perform its bodily deeds, and let our inner man be entirely dedicated to the service of God, and never lag behind this spiritual work of mental prayer, as the God-man Jesus commands us, saying in the Holy Gospel: "But you, when you pray, enter into your closet, and when you have shut your doors, pray to your Father who is in secret" ( Matthew 6:6 ). The closet of the soul is the body; our doors are the five bodily senses. The soul enters its cell when the mind does not wander here and there among worldly affairs and things, but is within our heart. Our senses are closed and remain so when we do not allow them to cling to external sensory things, and our mind thus remains free from all worldly attachments and unites with God our Father through hidden, mental prayer. "And your Father, who sees in secret, will reward you openly," adds the Lord. God, who knows all that is hidden, sees mental prayer and rewards it with great gifts.
For this prayer, too, is true and perfect prayer, which fills the soul with divine grace and spiritual gifts, just as ointment, the more tightly you stop a vessel, the more fragrant it makes that vessel. So too, the more firmly you imprison prayer within your heart, the more it abounds with divine grace. Blessed are those who master this heavenly practice, for with it they conquer every temptation of evil demons, as David conquered the proud Goliath. With it they quench the unruly desires of the flesh, as the three youths extinguished the flames of the furnace. By this practice of mental prayer, passions are tamed, as Daniel tamed wild beasts. With it they bring down the dew of the Holy Spirit into their hearts, as Elijah brought down rain on Mount Carmel. This mental prayer ascends to the very throne of God and is preserved in golden vials, and, like incense, it is fragrant before the Lord, as John the Theologian saw in the revelation: "And the twenty-four elders fell down before the Lamb, each having a harp, and golden vials full of incense, which are the prayers of the saints" ( Rev. 5:8 ). This mental prayer is a light that enlightens the human soul and ignites the heart with the fire of love for God. It is a chain that holds God in union with man and man with God. O, the incomparable grace of mental prayer! It places man in the position of constant interlocutor with God.
O, truly wondrous and marvelous thing! You interact with people physically, but converse with God mentally. Angels have no physical voice, but with their minds they offer unceasing praise to God. This is their entire work, and their entire life is dedicated to it. So it is with you, brother, when you enter your closet and close the door—that is, when your mind does not wander here and there, but enters within your heart, and your senses are enclosed and shielded from the things of this world, and thus you always pray—then you become like the holy angels, and your Father, who sees your secret prayer, which you offer Him in the secrecy of your heart, will reward you openly with great spiritual gifts. And what more do you desire from this, when, as I have said, you are always mentally before God and converse with Him unceasingly—conversing with God, without Whom no man can ever be blessed either here or in the next life. Finally, my brother, whoever you may be, when you take this book into your hands and, having read it, desire to experience in action the benefit to the soul that mental prayer brings, I fervently beg you, when you begin to say this prayer, do not forget to ask one cry: Lord have mercy! Raise up to God a petition for the sinful soul of him who labored over the compilation of this book, and of him who spent money on its printing and publication; for they have great need of your prayer, that they may find God's mercy for their souls, as you have for yours. May it be so! May it be so!
Source: https://azbyka.ru/otechnik/prochee/dobrotoljubie_tom_5/32