The following is an excerpt from Metropolitan Kallistos Ware (b. 1934) in his Introduction to On the Prayer of Jesus , by Ignatius Brianchaninov, Kallistos Ware, Father Lazarus.
“Ignatius [Brianchaninov] distinguishes three main stages or levels on this journey inwards, which he describes as “oral”, “mental”, and “cordial”; that is to say, prayer of the lips, prayer of the mind, and prayer of the heart”.
“The third degree of prayer is attained when not only does the mind or intellect [nous] recite the Jesus Prayer with full attentiveness, but it also descends into the heart and is united with it. In this way our invocation [of Lord, Jesus, Christ, Son of God] becomes prayer of the heart, or more exactly prayer of the mind in the heart. When the hesychast tradition speaks of the “heart” in this context, the word is to be understood in its full Hebraic sense, as found in Scripture: it signifies, not merely the emotions and affections, but the moral and spiritual center of the total person, the ground and focal point of our created being, the deep self. Prayer of the heart, then, is no longer prayer of the faculty alone, but prayer of the entire person, spirit, soul, and body together. It is precisely at this stage that prayer becomes not just something that we do but something that we are – something, moreover, that we are not just from time to time but continually. In this way St. Paul’s injunction becomes a realized fact: “Pray without ceasing” (1 Thess. 5:17). Nor is this all. Since the heart is not only the center of our created personhood but also the place where Christ and the Holy Spirit dwell within us, prayer of the heart is not so much something that we do as something that God does; not so much my prayer as the prayer of Christ in me (Gal. 2:20).”