“Angels do not have sensible voices, but mentally they offer up constant praise to God. This is their whole occupation; their entire life is dedicated to this. And you too, brother, when you enter your closet and shut the door, i.e. when your mind no longer wanders to and fro, but enters the inner recesses of your heart, and your senses are locked up and kept away from the things of the world, and in this manner you always pray, then you are like the holy angels, and your Father, seeing your secret prayer which you offer to Him out of the treasury of your heart, will bestow upon you openly great spiritual gifts.”
(St Gregory Palamas on the ‘Prayer of the Heart’)