Vigilance is a firm control of the mind. Posting it at the door of the heart… Strike the serpent on the head before he enters the cell. If the serpent enters, the struggle will be much more laborious.
This passage presents prosoche in its fullest Philokalic articulation: vigilance as an active, disciplined gatekeeping of the mind against intrusive thoughts and demonic suggestion before they penetrate the heart.
, Philokalia: The Bible of Orthodox Spirituality, 1998thesis