Brother, know that a man does not fall because he is weak, but because he forgets to stay watchful, and weakness is no shame, but forgetfulness is the wound through which the enemy enters. When the mind scatters into many things, the heart empties of the One, and he who does not guard the One becomes a slave to all. Do not fight thoughts as if they were stones, but look at them as shadows which, if you do not give them light, disappear. Remember that it is not the one who sees many miracles who is saved, but the one who keeps a single moment of humility.
Apophthegm
A brother asked the elder: Father, how can I cleanse my heart?
And the elder said to him: Cleanse your gaze first, and the heart will follow.
The brother did not understand and said within himself: How can the gaze go before the heart?
Pustia Inimii 