John Cassian on Fasting

“Bodily weakness is no hindrance to purity of heart, if only so much food is taken as the bodily weakness requires, and not what pleasure asks for.”

“The belly when filled with all kinds of food gives birth to seeds of wantonness, nor can the mind, when choked with the weight of food, keep the guidance and government of the thoughts. For not only is drunkenness with wine wont to intoxicate the mind, but excess of all kinds of food makes it weak and uncertain, and robs it of all its power of pure and clear contemplation.”

“On the manner of fasting a uniform rule cannot easily be observed, because everybody has not the same strength; nor is it like the rest of the virtues, acquired by steadfastness of mind alone. And therefore, because it does not depend only on mental firmness, since it has to do with the possibilities of the body, we have received this explanation concerning it which has been handed down to us, viz.: that there is a difference of time, manner, and quality of the refreshment in proportion to the difference of condition of the body, the age, and sex: but that there is one and the same rule of restraint to everybody as regards continence of mind, and the virtue of the spirit.”

“Let us not believe that that external fast from visible food alone can possibly be sufficient for perfection of heart and purity of body unless with it there has also been united a fast of the soul. For the soul also has its foods which are harmful, fattened on which, even without superfluity of meats, it is involved in a downfall of wantonness. Slander is its food, and indeed one that is very dear to it. A burst of anger also is its food, even if it be a very slight one; yet supplying it with miserable food for an hour, and destroying it as well with its deadly savour. Envy is a food of the mind, corrupting it with its poisonous juices and never ceasing to make it wretched and miserable at the prosperity and success of another. Kenodoxia, i.e., vainglory is its food, which gratifies it with a delicious meal for a time; but afterwards strips it clear and bare of all virtue, and dismisses it barren and void of all spiritual fruit, so that it makes it not only lose the rewards of huge labours, but also makes it incur heavier punishments. All lust and shifty wanderings of heart are a sort of food for the soul, nourishing it on harmful meats, but leaving it afterwards without share of the heavenly bread and of really solid food. If then, with all the powers we have, we abstain from these in a most holy fast, our observance of the bodily fast will be both useful and profitable. For labour of the flesh, when joined with contrition of the spirit, will produce a sacrifice that is most acceptable to God, and a worthy shrine of holiness in the pure and undefiled inmost chambers of the heart.”