Being rendered stupid by dullness and as it were smitten with blindness, we can see nothing in ourselves but capital offences.
[…] And if we find that even for a short time we are free from these we at once imagine that there is no sin at all in us.
Accordingly we are distinguished from the number of those who see, because we do not see the many small stains, which are crowded together in us.
We are not smitten with saving contrition if the malady of vexation overtakes our thoughts, nor are we sorry that we are struck by the suggestions of vainglory.
Nor do we weep over our prayers offered up so tardily and coldly, nor consider it a fault if while we are singing or praying, something else besides the actual prayer or Psalm fills our thoughts.
Nor are we horrified because we do not blush to conceive many things which we are ashamed to speak or do before men, in our heart, which, as we know, lies open to the Divine gaze.
Nor do we purge away the pollution of filthy dreams with copious ablutions of our tears, nor grieve that in the pious act of almsgiving when we are assisting the needs of the brethren…, the brightness of our cheerfulness is clouded over by a stingy delay.
Nor do we think that we are affected by any loss when we forget God and think about things that are temporal and corrupt, so that these words of Solomon fairly apply to us: “They smite me but I have not grieved, and they have mocked me, but I knew it not.”
On the other hand, there are those who make the sum of all their joy and delight and bliss consist in the contemplation of divine and spiritual things alone.
If they are unwillingly withdrawn from them even for a short time by thoughts that force themselves upon them, they punish this as if it were a kind of sacrilege in them.
They avenge it by immediate chastisement, and in their grief that they have preferred some worthless creature (to which their mental gaze was turned aside) to their Creator.
They charge themselves with…impiety, and although they turn the eyes of their heart with the utmost speed to behold the brightness of the Divine Glory, yet they cannot tolerate even for a very short time the darkness of carnal thoughts, and execrate whatever keeps back their soul’s gaze from the true light.
John Cassian (c. 360-435): Conferences 23, 7-8.