The man who has struggled bravely with the passions of the body, has fought ably against unclean spirits, and has expelled from his soul the conceptual images they provoke, should pray for a pure heart to be given him and for a spirit of integrity to be renewed within him (Psalm 51:10). In other words, he should pray that by grace he may be completely emptied of evil thoughts and filled with divine thoughts, so that he may become a spiritual world of God, splendid and vast, wrought from moral, natural and theological forms of contemplation.
~St Maximos the Confessor
Prayerful Life 