This will be the sign for you when you have drawn near to entering into that region [of truth]. When grace has begun to open your eyes to perceive an exact vision of these things, then your eyes will begin to shed tears until your cheeks are washed by their abundance, and the fervor of the senses will be slowed that they may profitably be restrained within you. If there is one who teaches you other than this, do not believe him. But you are not permitted to seek another indication from the body besides tears as a manifest sign of the perception of truth, unless in the silence of the activity of the members of the body. This happens when the mind is raised above existing things, and the body ceases from tears and perception and any movement except physical vitality.
St. Isaac of Nineveh,