In the First Epistle to the Thessalonians the Apostle Paul says: "Pray without ceasing." How then, is one to pray unceasingly? By often repeating the Jesus Prayer: "Lord Jesus Christ, Son of God, have mercy on me." By becoming accustomed to this appeal, great consolation and the need to continually make this petition will be felt within, and it will be carried on, as if of itself, within one.
Although in the beginning the enemy of the human race will offer hindrances to this, by causing great weariness, indolence, boredom and overcoming sleep, having withstood all these with the help of God, one will receive peace of soul, spiritual joy, a benevolent disposition towards people, purification of thought, and gratitude towards God. In the very Name of Jesus a great and graceful power is present Many holy and righteous people advise repeating the Jesus Prayer as frequently as possible; without interruption. It is necessary for everyone, whether eating, drinking, sitting, serving, travelling, or in doing anything, to ceaselessly lament: "Lord Jesus Christ, Son of God, have mercy on me" in order that the Name of the Lord Jesus Christ, in descending into the depths of our hearts, may humble the serpent of destruction, and save and enlighten the soul.
St. Seraphim of Sarov: " 'Lord Jesus Christ, Son of God, have mercy on me, a sinner.' Let your attention and instruction be centered on this. Walking, eating, standing in church before the beginning of the service, continue with the prayer; on entering and departing keep this prayer on your lips and within your heart. In such a manner, with the invocation of the Name of God you will find peace, you will attain to purity of spirit and body; and the Holy Spirit, the Origin of all good, will make for Himself a dwelling within you and will guide you in all piety and purity."
Bishop Theophanes the Recluse: "To more conveniently become accustomed to remembering God, the fervent Christian has a special means, namely, to repeat ceaselessly a brief prayer of two or three words. Mostly this is 'Lord, have mercy.' or 'Lord Jesus Christ, Son of God, have mercy on me, a sinner.' If you have not yet heard of this, then hear it now, and if you have not done it, then begin from this hour to do it."
Those who have truly decided to serve the Lord God must train themselves in the rememberance of God and in unceasing prayer to Jesus Christ, saying mentally: "Lord Jesus Christ, Son of God, have mercy on me, a sinner."
Through such activity, and by guarding oneself from distraction, and with the preservation of peace in one's conscience, it is possible to draw near to God and to be united with Him. For, according to the words of St. Isaac the Syrian, "Except for unceasing prayer we cannot draw near to God" (St. Seraphim of Sarov).

Fr. John of Kronstadt also counselled frequently the use of the Prayer of Jesus.