One bread, one body
"This special closeness which comes about in Eucharistic 'communion' cannot be adequately understood or fully experienced apart from ecclesial communion. I emphasized this repeatedly in my Encyclical Ecclesia de Eucharistia. The Church is the Body of Christ: we walk 'with Christ' to the extent that we are in relationship 'with his body.' Christ provided for the creation and growth of this unity by the outpouring of his Holy Spirit. And he himself constantly builds it up by his Eucharistic presence. It is the one Eucharistic bread which makes us one body. As the Apostle Paul states: “Because there is one bread, we who are many are one body, for we all partake of the one bread” (1 Corinthians 10:17). In the mystery of the Eucharist Jesus builds up the Church as a communion, in accordance with the supreme model evoked in his priestly prayer: 'Even as you, Father, are in me, and I in you, that they may also be in us, so that the world may believe that you have sent me' (John 17:21)."
John Paul II, Apostolic Letter Mane Nobiscum Domine, 20