Talking with Geronta Pavlos of Sinai (# 15):

Q Does the Jesus Prayer empty the mind?
A It doesn’t empty the mind, it fills the mind. It fills it with the presence of God, with His grace. The name of Christ has such power that just by pronouncing it, with its grace it sanctifies us and elevates us.
Q Simply by us pronouncing it, without trying to understand the meaning of the name?
A Yes.
Q One often reads that we are to confine our mind within the words of the prayer.
A That is not an easy thing! In order to reach that point requires much work! Because the mind wanders; you can be saying the prayer and your mind leaves.
Q Is it better therefore to say the prayer with our voice or just in our mind?
A Each one as he can. The mystery of freedom exists here too. God respects the freedom of the person in every way, because He wants us to come near to Him freely. Therefore [one prays] as he can, according to his own strengths and abilities, do you understand?
From Questions and Answers in FMSM News Blog: