FASTING: St. Leo the Great, 5th century

From a sermon by Saint Leo the Great, pope (5th cent.)
Purification of Spirit through Fasting and Almsgiving

Dear friends, at every moment the earth is full of the mercy of God, and nature itself is a lesson for all the faithful in the worship of God. The heavens, the sea and all that is in them bear witness to the goodness and omnipotence of their Creator, and the marvelous beauty of the elements as they obey him demands from the intelligent creation a fitting expression of its gratitude.
But with the return of that season marked out in a special way by the mystery of our redemption, and of the days that lead up to the paschal [Easter] feast, we are summoned more urgently to prepare ourselves by a purification of spirit. The special note of the paschal feast is this: the whole Church rejoices in the forgiveness of sins. It rejoices in the forgiveness not only of those who are then reborn in holy baptism but also of those who are already numbered among God's adopted children.
Initially, men are made new by the rebirth of baptism. Yet there still is required a daily renewal to repair the shortcomings of our mortal nature, and whatever degree of progress has been made there is no one who should not be more advanced. All must therefore strive to ensure that on the day of redemption no one may be found in the sins of his former life.
Dear friends, what the Christian should be doing at all times should be done now with greater care and devotion, so that the Lenten fast enjoined by the apostles may be fulfilled, not simply by abstinence from food but above all by the renunciation of sin.
There is no more profitable practice as a companion to holy and spiritual fasting than that of almsgiving. This embraces under the single name of mercy many excellent works of devotion, so that the good intentions of all the faithful may be of equal value, even where their means are not. The love that we owe both God and man is always free from any obstacle that would prevent us from having a good intention. The angels sang: Glory to God in the highest, and peace to his people on earth. The person who shows love and compassion to those in any kind of affliction is blessed, not only with the virtue of good will but also with the gift of peace.
The works of mercy are innumerable. Their very variety brings this advantage to those who are true Christians, that in the matter of almsgiving not only the rich and affluent but also those of average means and the poor are able to play their part. Those who are unequal in their capacity to give can be equal in the love within their hearts.