Christ prayed to His heavenly Father: “The glory which Thou hast given Me, I have given to them; that they may be one, as We also are one: I in them, and Thou in Me; that they may be made perfect in one” (Jn 17:22). And again: “Not for them only do I pray, but for those also who through their word shall believe in Me; that they all may be one, as Thou, Father, in Me, and I in Thee; that they also may be one in Us; that the world may believe that Thou hast sent Me” (Jn 17:20-21).
St. John Chrysostom explains: “We are ourselves the body of Christ. For what is the bread upon the altar? The body of Christ. And what do they become that receive it? The body of Christ; not many bodies, but one body. As the bread is a whole composed of many grains, and the separate grains nowhere appear, and in their union do not show the distinction though they continue to exist, so we are united amongst ourselves and with Christ. For you are not nourished by one body, and another one by another body, but all by the same body. And therefore the Apostle says: ‘We all are partakers of the same bread; but of this we all are made one body’ (1 Cor 10:17).”
Christ said: “He that eateth My flesh and drinketh My blood abideth in Me, and I in him” (Jn 6:56). St. Cyril comments: “It is of importance to notice that Christ will be in us, as He Himself says, not merely by a certain relation of love, but by a real union. For as two pieces of wax placed and molten together are made one whole, so are we united to Christ by the reception of His body and blood.”
“The natural bread is also united with the body of him that partakes of it. But since it is a dead and perishable bread, it cannot convert the bodies of the partakers into its own substance. The Body of Christ, however, is a living, undivided, imperishable Bread, and therefore it unites with itself the bodies of those that receive it, makes them its members, and fills them with the plenitude of Divine life. Our Lord said: ‘I am the Vine, and you are the branches’ (Jn 15:5). Thus the Vine feeds with its sap the branches united with it, and penetrates and vivifies them with its own vitality.”
Quotations from Alice Lady Lovat, The Marvels of Divine Grace: Meditations Based on the “Glories of Divine Grace” (Original Treatise by Fr. Nieremberg, S.J., Entitled “Del Aprecio y Estima de la Divina Gracia”) (London: R. & T. Washbourne, Ltd., 1917).