We know that God forbade our first parents in Paradise under the penalty of death to eat of the tree of knowledge of good and evil thus you see the precept of abstaining and fasting is of a very ancient date for it was the first precept given by God to man; and the first good work that man should have done was to abstain. From this it naturally follows that abstaining or fasting pleases God; but it displeases the devil, else he would not have seduced our first parents and persuaded them to transgress the precept. We ought to consider this fast strictly in order to please God and displease the devil.
The prophet Jonas, by God's commandment had already announced to the city of Nineve its destruction. What saved that city? Fasting. Neither king, nor people, nor beast took either food or drink; all from the highest to the lowest did penance, and God spared their city.
At the inauguration of the new law, we first meet with St. John the Baptist, of whom an angel said to Zachary before he was conceived in his mother's womb that he would drink no wine nor strong drink. In fact, the whole life of this greatest of all prophets was a continual fast. John had his garment of camel's hair, a leathern girdle about his loins and his meat was locusts and wild honey. (Matt. 3:4.).
Jesus Christ Himself gives us the example by His fasting, for, as the gospel tells us, He fasted in the desert forty days and forty nights so austerely that during this long space of time he abstained entirely from food and drink. After considering these things who can doubt that fasting is a work pleasing to God?
Fasting has the virtue of cleansing from sin. The Jews believed this and therefore their days of penance were also fast days. "Every soul that is not afflicted on this day (the great day of propitiation) shall perish from among his people" (Leviticus 23, 29) Among Christians also fasting was considered a means of obtaining from God the forgiveness of sin. St. Basil says, "fast because you have sinned. By fasting, you will blot out the sins which you have committed against God." This however is not to be understood as if fasting effected immediately that forgiveness of sins as the sacrament of penance does. Fasting has not this virtue but if we fast with a contrite heart, we may confidently hope that God will give a special grace to us to make a good confession and obtain the forgiveness of all our sins. By penitential fasting as well as by other works of penance we can blot out venial sins.
Strictly observe the ecclesiastical precepts of fasting during this holy season, for it is acceptable to God and profitable to you. But be not satisfied with merely abstaining from flesh meat on the days appointed, and in depriving yourselves of the usual quantity of meat and drink, but unite the spiritual fast with the corporal; carefully avoid sin, mortify your inordinate inclinations, bridle your senses, the ears, eyes, and tongue; live as much as possible a retired life, and occupy yourselves with God and the concerns of your soul. This is the way to make your fast truly holy and salutary and one that will merit the grace of God and life everlasting. Amen.