Just as it is impossible for the eye to perceive sensible objects without the light of the sun, so the human intellect cannot engage in spiritual contemplation without the light of the Spirit. For physical light naturally illuminates the senses so that they may perceive physical bodies; while spiritual light illumines the intellect so that it can engage in contemplation and thus grasp what lies beyond the senses.
~St Maximos the Confessor
Prayerful Life 