Some people assert that the Jesus Prayer is always, or nearly always, followed by delusion, and strictly forbid the use of this prayer.
To accept such an idea and to make such a prohibition constitutes a terrible blasphemy - illusion of an utterly deplorable character. Our Lord Jesus Christ is the one source of our salvation, the only means whereby we can be saved: and His human Name has received from His divinity an unlimited and holy power to save us. How can this power, working for salvation - the only power that gives salvation - become distorted and work for perdition? Such a suggestion is absurd. It is melancholy, blasphemous, soul-destroying nonsense. Those who adopt this line of argument are indeed beguiled by the devil, and deceived by the spurious reasoning which comes from Satan.
Examine all the Holy Scriptures: you will find the Name of the Lord exalted and glorified everywhere in them, and its saving power extolled throughout. Study the writings of the Fathers and you will see that all of them, without exception, suggest and advise the practice of the Jesus Prayer, calling it a weapon stronger than any other in heaven or on earth; a gift of God, an inalienable heritage, one of the culminating and most exalted bequests of the God-Man, a solace most sweet and full of love, a sure pledge. Finally, tum to the canonical decrees of the Eastern Orthodox Church and you will find that in the case of all its illiterate children, both monks and laymen, the Church has established the recitation of the Jesus Prayer as a substitute for the reading of psalms and prayers in one's own cell or room.
What weight, then, can there be in the recommendations of a few blind men, extolled and applauded by others equally blind, as compared with the unanimous testimony of the Holy Scriptures, of all the Holy Fathers, and of the canonical decrees of the Church concerning the Jesus Prayer?
The correct practice of the Jesus Prayer proceeds naturally from correct notions about God, about the most holy Name of the Lord Jesus, and about man's relationship to God.
The Name of our Lord Jesus Christ is a divine Name. The power and effect of that Name are divine, omnipotent and salvific, and transcend our ability to comprehend it. With faith therefore, with confidence and sincerity, and with great piety and fear ought we to proceed to the doing of the great work which God has entrusted to us: to train ourselves in prayer by using the Name of our Lord Jesus Christ.
Certain people have developed an unfortunate prejudice against the Jesus Prayer, although they lack the personal knowledge that comes from a correct and long practice of the Prayer. It would have been much more safe and sensible for such people to refrain from making any judgement on the subject: they should realize their complete ignorance of this sacred task, rather than take upon themselves the mission of preaching against the practice of the Jesus Prayer, and of denouncing this holy prayer as the cause of diabolic illusion and the soul's perdition. I must say to them by way of warning that to censure the prayer which uses the Name of Jesus, and to ascribe a harmful effect to this Name, is as bad as the censure which the Pharisees passed upon the miracles accomplished by Our Lord. This ignorant and blasphemous theorizing against the Jesus Prayer has all the character of heretical pseudo-philosophy.
St. Ignatius Brianchaninov, On Practicing Jesus Prayer.