From a sermon on the beatitudes by Saint Leo the Great, pope
(Sermo 95, 8-9: PL 54, 465-466)
Those who love your law shall have abundant peace
The blessedness of seeing God is justly promised to the pure of heart. For the eye that is unclean would not be able to see the brightness of the true light, and what would be happiness to clear minds would be a torment to those that are defiled. Therefore, let the mists of worldly vanities be dispelled, and the inner eye be cleansed of all the filth of wickedness, so that the soul’s gaze may feast serenely upon the great vision of God.