It is not the enemy that is outside us whom we need to fear; there is an enemy in our very selves: daily within us an internal war is waged. When the enemy within is conquered, all our foes without are rendered feeble, and Christ’s soldier will find all things at peace, and all subdued. We shall have no external foe to fear if what is within is conquered, and subdued to the spirit.
~St John Cassian
Prayerful Life 