As then we must with the whole heart obey the Divine commands and sound doctrine, so we must use all foresight in abstaining from wicked imaginations. For the mind then only keeps holy and spiritual fast when it rejects the food of error and the poison of falsehood, which our crafty and wily foe plies us with more treacherously now, when by the very return of the venerable Festival, the whole church generally is admonished to understand the mysteries of its salvation. For he is the true confessor and worshipper of Christ's resurrection, who is not confused about His passion, nor deceived about His bodily nativity.
Leo the Great, Sermon VIII on Lent
