Nēpsis, sobriety or watchfulness, is a key virtue of the Philokalia: the guard of the heart, which notices thoughts as they arise and refuses entry to those that lead away from God. Hesychius of Sinai called it a spiritual method that frees the person from passionate thoughts.
Nepsis
Watchfulness: sober, vigilant attention to the movements of the heart and mind, guarding against distracting thoughts.
Also: watchfulness