Encyclical on the Holy Eucharist - Parts 39 & 40

39. Furthermore, given the very nature of ecclesial communion and its relation to the sacrament of the Eucharist, it must be recalled that “the Eucharistic Sacrifice, while always offered in a particular community, is never a celebration of that community alone. In fact, the community, in receiving the Eucharistic presence of the Lord, receives the entire gift of salvation and shows, even in its lasting visible particular form, that it is the image and true presence of the one, holy, catholic and apostolic Church”.⁷⁹ From this it follows that a truly Eucharistic community cannot be closed in upon itself, as though it were somehow self-sufficient; rather it must persevere in harmony with every other Catholic community. 

The ecclesial communion of the Eucharistic assembly is a communion with its own Bishop and with the Roman Pontiff. The Bishop, in effect, is the visible principle and the foundation of unity within his particular Church.⁸⁰ It would therefore be a great contradiction if the sacrament par excellence of the Church's unity were celebrated without true communion with the Bishop. As Saint Ignatius of Antioch wrote: “That Eucharist which is celebrated under the Bishop, or under one to whom the Bishop has given this charge, may be considered certain”.⁸¹ Likewise, since “the Roman Pontiff, as the successor of Peter, is the perpetual and visible source and foundation of the unity of the Bishops and of the multitude of the faithful”,⁸² communion with him is intrinsically required for the celebration of the Eucharistic Sacrifice. Hence the great truth expressed which the Liturgy expresses in a variety of ways: “Every celebration of the Eucharist is performed in union not only with the proper Bishop, but also with the Pope, with the episcopal order, with all the clergy, and with the entire people. Every valid celebration of the Eucharist expresses this universal communion with Peter and with the whole Church, or objectively calls for it, as in the case of the Christian Churches separated from Rome”.⁸³ 

40. The Eucharist creates communion and fosters communion. Saint Paul wrote to the faithful of Corinth explaining how their divisions, reflected in their Eucharistic gatherings, contradicted what they were celebrating, the Lord's Supper. The Apostle then urged them to reflect on the true reality of the Eucharist in order to return to the spirit of fraternal communion (cf. 1 Cor 11:17- 34). Saint Augustine effectively echoed this call when, in recalling the Apostle's words: “You are the body of Christ and individually members of it” (1 Cor 12: 27), he went on to say: “If you are his body and members of him, then you will find set on the Lord's table your own mystery. Yes, you receive your own mystery”.⁸⁴ And from this observation he concludes: “Christ the Lord... hallowed at his table the mystery of our peace and unity. Whoever receives the mystery of unity without preserving the bonds of peace receives not a mystery for his benefit but evidence against himself”.⁸⁵