Never confuse the person, formed in the image of God, with the evil that is in him: because evil is but a chance misfortune, an illness, a devilish attack. But the very essence of the person is the image of God, and this remains in him despite every disfigurement.
St. John of Kronstadt
Our holy fathers have renounced all other spiritual work and concentrated wholly on this one doing, that is, on guarding the heart, convinced that, through this practice, they would easily attain every other virtue, whereas without it not a single virtue can be firmly established.