Qui manducat meam carnem, et bibit meum sanguinem in me manet, et ego in eo, dicit Dominus. (Communion antiphon for the Ninth Sunday after Pentecost - cf. John vi, 57: He that eateth my flesh, and drinketh my blood, abideth in me, and I in him, saith the Lord.)
The venerable Sacrament of the Eucharist is both the source and the pledge of blessedness and of glory, and this, not for the soul alone, but for the body also. For it enriches the soul with an abundance of heavenly blessings, and fills it with a sweet joy which far surpasses man's hope and expectations; it sustains him in adversity, strengthens him in the spiritual combat, preserves him for life everlasting, and as a special provision for the journey accompanies him thither. And in the frail and perishable body that divine Host, which is the immortal Body of Christ, implants a principle of resurrection, a seed of immortality, which one day must germinate. That to this source man's soul and body will be indebted for both these boons has been the constant teaching of the Church, which has dutifully reaffirmed the affirmation of Christ: "He that eateth my flesh and drinketh my blood hath everlasting life; and I will raise him up at the last day" (John vi, 55).
In connection with this matter it is of importance to consider that in the Eucharist, seeing that it was instituted by Christ as "a perpetual memorial of His Passion", is proclaimed to the Christian the necessity of a salutary selfchastisement. For Jesus said to those first priests of His: "Do this in memory of Me" (Luke xxii, 18); that is to say, do this for the commemoration of My pains, My sorrows, My grievous afflictions, My death upon the Cross. Wherefore this Sacrament is at the same time a Sacrifice, seasonable throughout the entire period of our penance; and it is likewise a standing exhortation to all manner of toil, and a solemn and severe rebuke to those carnal pleasures which some are not ashamed so highly to praise and extol: "As often as ye shall eat this bread, and drink this chalice, ye shall announce the death of the Lord, until He come" (1 Cor. xi, 26).
Furthermore, if anyone will diligently examine into the causes of the evils of our day, he will find that they arise from this, that as charity towards God has grown cold, the mutual charity of men among themselves has likewise cooled. ... Hence frequent disturbances and strifes between class and class: arrogance, oppression, fraud on the part of the more powerful: misery, envy, and turbulence among the poor. These are evils for which it is in vain to seek a remedy in legislation, in threats of penalties to be incurred, or in any other device of merely human prudence. Our chief care and endeavour ought to be... to secure the union of classes in a mutual interchange of dutiful services, a union which, having its origin in God, shall issue in deeds that reflect the true spirit of Jesus Christ and a genuine charity. This charity Christ brought into the world, so that with it He would have all hearts on fire. For it alone is capable of affording to soul and body alike, even in this life, a foretaste of blessedness; since it restrains man's inordinate self-love, and puts a check on avarice, which "is the root of all evil" (1 Tim. vi, 10).
And whereas it is right to uphold all the claims of justice as between the various classes of society, nevertheless it is only with the efficacious aid of charity, which tempers justice, that the "equality" which St. Paul commended (2 Cor. viii, 14), and which is so salutary for human society, can be established and maintained. This then is what Christ intended when he instituted this Venerable Sacrament, namely, by awakening charity towards God to promote mutual charity among men. ... For in [this Sacrament] He has not only given a splendid manifestation of His power and wisdom, but "has in a manner poured out the riches of His divine love towards men" (Concil of Trent, Session XIII). ...
Besides all this, the grace of mutual charity among the living, which derives from the Sacrament of the Eucharist so great an increase of strength, is further extended by virtue of the Sacrifice to all those who are numbered in the Communion of Saints. For the Communion of Saints, as everyone knows, is nothing but the mutual communication of help, expiation, prayers, blessings, among all the faithful, who, whether they have already attained to the heavenly country, or are detained in the purgatorial fire, or are yet exiles here on earth, all enjoy the common franchise of that city whereof Christ is the head, and whose constitution is charity.