In Baptism we have been called to form but one body. The Eucharist fulfills this call: "The cup of blessing which we bless, is it not a participation in the blood of Christ? The bread which we break, is it not a participation in the body of Christ? Because there is one bread, we who are many are one body, for we all partake of the one bread” (1 Cor 10:16-17):
If you are the body and members of Christ, then it is your sacrament that is placed on the table of the Lord; it is your sacrament that you receive. To that which you are you respond “Amen” (“yes, it is true!”) and by responding to it you assent to it. For you hear the words, “the Body of Christ” and respond “Amen.” Be then a member of the Body of Christ that your Amen may be true (St. Augustine, Sermon 272: PL 38, 1247).