St Leo the Great: Fasting from Heresy

According to St Leo the Great, the Lenten fast is a fast from error as well as a fast from food and other worldly pleasures.

When he speaks of “error”, Leo always means error concerning the fact that Jesus Christ is truly human and truly divine, that he truly suffered and died for our redemption, that he truly rose from the dead and ascended into heaven, and that he is truly present in the Eucharist.

For Leo, Lent prepares us to participate worthily in the Easter festival, and this preparation involves both “mortification of the flesh” and “purification of the mind”.

Leo also sees Lent as a time when the devil attacks Christians and the Church with renewed hostility, and these attacks include temptations to heresy. Firm adhesion to the teachings of the Creed helps to defeat the wiles of the devil, and at the same time prepares us for the outpouring of Christ’s grace at Easter.

From Sermon 46,1; 3.

because the right practice of abstinence is needful not only to the mortification of the flesh but also to the purification of the mind, we desire your observance to be so complete that, as you cut down the pleasures that belong to the lusts of the flesh, so you should banish the errors that proceed from the imaginations of the heart. For he whose heart is not polluted with false belief prepares himself with true and reasonable purification for the paschal feast, in which all the mysteries of our religion meet together.

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.

This belief in the Lord’s incarnation, dearly-beloved, through which the whole Church is Christ’s body hold firm with heart unshaken and abstain from all the lies of heretics, and remember that your works of mercy will only then profit you, and your strict continence only then bear fruit, when your minds are unsoiled by any defilement from wrong opinions. Cast away the arguments of this world’s wisdom, for God hates them, and none can arrive by them at the knowledge of the Truth, and keep fixed in your mind that which you say in the Creed.