[I]t is but godly and just that we too should help others with that which the Heavenly Father has mercifully bestowed on us…, from which the hunger of the needy and the weak is satisfied from which the wants of the stranger are relieved, from which the desire of the sick is gratified. For these men God has in His justice permitted to be afflicted with various troubles, that He might both crown the wretched for their patience and the merciful for their loving-kindness.
And while all seasons are opportune for this duty, beloved, yet this present season [of the Ember days of Advent] is specially suitable and appropriate…. For forgiveness of sins is most efficaciously prayed for with almsgiving and fasting, and supplications that are winged by such aids mount swiftly to God’s ears: since as it is written, the merciful man does good to his own soul (Proverbs 11:17), and nothing is so much a man’s own as that which he spends on his neighbour. For that part of his material possessions with which he ministers to the needy, is transformed into eternal riches….
“But at all these acts of godliness, dearly-beloved, which commend us more and more to God, there is no doubt that our enemy, who is so eager and so skilled in harming us, is aroused with keener stings of hatred, that under a false profession of the Christian name he may corrupt those whom he is not allowed to attack with open and bloody persecutions, and for this work he has heretics in his service whom he has led astray from the catholic Faith, subjected to himself, and forced under various errors to serve in his camp….
Display then a holy zeal of religious vigilance, and let all the faithful rise in one body against these savage enemies of their souls. For the merciful God has delivered a certain portion of our noxious foes into our hands in order that by revelation of the danger the utmost caution might be aroused. Let not what has been done suffice, but let us persevere in searching them out: and by God’s aid the result will be not only the continuance in safety of those who still stand, but also the recovery from error of many who have been deceived by the devil’s seduction. And the prayers, and alms, and fasts that you offer to the merciful God shall be the holier for this very devotion, when this deed of faith also is added to all your other godly duties.
On [Ember] Wednesday and Friday, therefore, let us fast, and on Saturday let us keep vigil in the presence of the most blessed Apostle Peter; who, as we experience and know, watches unceasingly like a shepherd over the sheep entrusted to him by the Lord, and who will prevail in his entreaties that the Church of God, which was founded by his preaching, may be free from all error, through Christ our Lord. Amen.
— Pope St. Leo I, Sermon 16: On the Fast of the Tenth Month
If you have gained any knowledge of insight from this passage, I pray that you would in turn produce a harvest of action in accord with it.