The necessity of fasting is twofold, derived from divine law and human law. Of the divine, the prophet Joel speaks: “Be converted to me with your whole heart, in fasting, and in weeping, and in mourning.” The same language is used by the prophet Jonah, who testifies that the Ninevites, in order to appease the anger of God, proclaimed a fast in sackcloth. And yet, there was not any positive law on fasting then. The same may be learned from the words of our Lord in St. Matthew’s Gospel: “But thou, when thou fastest, anoint thy head and wash thy face, that thou appear not to men to fast, but to thy Father, who is in secret; and thy Father, who seeth in secret, will repay thee.”
St. Augustine thus speaks in his letter to Casulanus:
“In the Gospels and epistles, and in the whole of the New Testament, I see fasting is a precept. But on certain days we are not commanded to fast; and the particular days on which we must [fast] are not defined by our Lord or the apostles.”St. Augustine, Letter 36, ch. 11.
St. Leo also says in his sermon on fasting:
“Those which were figures of future things have passed away, what they signified being accomplished. But the utility of fasting is not done away with in the New Testament; but it is piously observed that fasting is always profitable both to the soul and body. And because the words ‘Thou shalt adore the Lord thy God, and serve Him alone’ . . . were given for the knowledge of Christians, so in the same Scripture, the precept concerning fasting cannot be interpreted away.”St. Leo the Great, Fourth Sermon on the December Fast, ch. 2.
St. Leo does not mean to say here that Christians must fast at the same times the Jews were accustomed to fast. But the precept of fasting given to the Jews is to be observed by Christians according to the determination of the pastors of the Church, as to time and manner.
Fruits of Fasting
The fruits and advantages of fasting can easily be proved. First, fasting is most useful in preparing the soul for prayer, and the contemplation of divine things, as the angel Raphael says: “Prayer is good with fasting.” Thus for forty days, Moses prepared his soul by fasting before he presumed to speak with God.
I cannot forbear quoting the words of St. John Chrysostom: “Fasting is the support of our soul: it gives us wings to ascend on high, and to enjoy the highest contemplation.”
Another advantage of fasting is that it tames the flesh; and such a fast must be particularly pleasing to God, because He is pleased when we crucify the flesh with its vices and concupiscences, as St. Paul teaches us in his letter to the Galatians; and for this reason, he himself says, “But I chastise my body, and bring it into subjection, lest perhaps, when I have preached to others, I myself should become a castaway.” And of the advantages of fasting in this respect, the whole Church in the office sings, “Moderation in food and drink tames the pride of the flesh.”
Fasting Honors God
Another advantage is that we honor God by our fasts when we fast for His sake. Thus the apostle Paul speaks in his letter to the Romans: “I beseech you therefore, brethren, by the mercy of God, that you present your bodies as a living sacrifice, holy, pleasing unto God, your reasonable service.” In the Greek, “reasonable service” (logiken latreian) is “reasonable worship”; and St. Luke speaks of this worship when mentioning the prophetess Anna: “And she was a widow until fourscore and four years, who departed not from the temple, by fasting and prayers serving night and day.”
The great Council of Nicaea calls the fast of Lent “a clean and solemn gift, offered by the Church to God.” St. Leo, in his second sermon on fasting, says, “For the sure reception of all its fruits, the sacrifice of abstinence is most worthily offered to God, the giver of them all.”
Fasting Satisfies God
A fourth advantage of fasting is that it is a satisfaction for sin. Many examples in Scripture prove this. The Ninevites appeased God by fasting, as Jonah testifies. The Jews did the same, for by fasting with Samuel, they appeased God and gained victory over their enemies. The wicked king Ahab, by fasting and sackcloth, partly satisfied God. In the times of Judith and Esther, the Hebrews obtained mercy from God by no other sacrifice than fasting, weeping, and mourning.
This is also the constant doctrine of the holy Fathers. Tertullian says, “As we refrain from the use of food, so our fasting satisfies God.” St. Cyprian: “Let us appease the anger of an offended God by fasting and weeping, as He admonishes us.” St. Ambrose also says, “Fasting is the death of sin, the destruction of our crimes, and the remedy of our salvation.” St. Jerome remarks, “Fasting and sackcloth are the arms of penance, the help of sinners.” St. Augustine likewise says, “No one fasts for human praise, but for the pardon of his sins.”
Lastly, fasting is meritorious, and is very powerful in obtaining divine favors. Anna, although she was barren, deserved by fasting to have a son. So St. Jerome thus interprets these words of Scripture: “She wept and did not take food, and thus Anna, by her abstinence, deserved to bring forth a son.” Sarah, by a three days’ fast, was delivered from a devil, as we read in the book of Tobit.
But there is a remarkable passage in the Gospel of St. Matthew on fasting: “But thou, when thou fastest, anoint thy head and wash thy face, that thou appear not to men to fast, but to thy Father, who is in secret; and thy Father, who seeth in secret, will repay thee.” The words “will repay thee” signify “will give thee a reward,” for they are opposed to these other words: “For they disfigure their faces, that they may appear to men to fast. Amen, I say to you, they have received their reward.” Wherefore hypocrites, by their fasting, receive their reward: human praise; the just, by fasting, receive their reward also: divine praise.
Many are the testimonies of the holy Fathers on this point. When St. John was about to write his Gospel, he underwent a solemn fast, so that he might deserve to receive the grace of writing well. Tertullian says, “Fasting obtains of God a knowledge even of His mysteries.”
How We Should Fast
Here, then, we have seen the necessity and the fruits of fasting. I will now briefly explain the manner in which we must fast, so that our fasting may be useful in enabling us to lead a good life and, by this means, to die a good death.
Many fast on all the days appointed by the Church: on vigils, on Ember Days, and during Lent. And some fast of their own accord in Advent also, so that they may piously prepare themselves for the Nativity of our Lord; or on Fridays, in memory of our Lord’s Passion; or on Saturdays, in honor of the Blessed Virgin Mother of God.
The chief end of fasting is the mortification of the flesh, so that the spirit may be strengthened more. For this purpose, we must use only spare and unsavory diet. And this our mother the Church points out since she commands us to take only one “full” meal in the day, and then not to eat meat. Now, this is certainly not observed by those who, on their fasting days, eat as much in one meal, as they do on other days at their dinner and supper together; and who, at that one meal, prepare so many dishes of different fishes and other things to please their palate, that it seems to be a dinner intended, not for weepers and fasters, but for a nuptial banquet that is to continue throughout most of the night! Those who fast thus certainly do not derive the least fruit from their fasting.
Nor do those derive any fruit who, although they may eat more moderately, yet on fasting days, do not abstain from games, parties, quarrels, dissensions, lascivious songs, and immoderate laughter; and what is still worse, commit the same crimes as they would on ordinary days.
Those pious people who wish their fasting to be pleasing to God and useful to themselves should avoid these and other such sins. They may then hope to live well and die a holy death.
We also recommend St. Robert Bellarmine’s A Commentary on the Book of Psalms.