We write of what we know; and for those who want to understand what we say, we bear witness to all that we have seen as we journeyed on our path. He Himself has declared: ‘If a man not abide in Me, he is cast out as a branch; and men gather it, and cast it into the fire, and it is burned. If he abides in Me, I abide in him (cf. John 15:5-6). The sun cannot shine without light; nor can the heart be cleansed of the stain of destructive thoughts without invoking in prayer the Name of Jesus. This being the case, we should use that Name as we do our own breath. For that Name is light, while the evil thoughts are darkness, it is God and Master, while evil thoughts are slaves and demons.
St. Hesychius the Presbyter,
On Watchfulness and Holiness, 170.
(The Philokalia, Vol. I, trans. Palmer, et al)