"The Eucharist is our participation in the Easter mystery, and hence it is constitutive of the Church, the Body of Christ. This is why the Eucharist is necessary for salvation. The necessity of the Eucharist is identical with the necessity of the Church and vice versa. This is how we should understand the Lord's saying: 'Unless you eat the flesh of the Son of man and drink his blood, you have no life in you' (Jn 6:53). Hence we see the necessity, too, of a visible Church and a visible, concrete (and one might say 'institutional') unity. The most intimate mystery of communion between God and man is accessible in the sacrament of the Body of the Risen Lord; conversely, then, the mystery lays claim to our bodies and is realized in a Body. The Church, which is built upon the sacrament of the Body of Christ, must herself be a body. And she must be a single body, corresponding to Jesus Christ's uniqueness, a uniqueness which is reflected in unity and in the 'continuing in' the one, apostolic teaching."
-Joseph Cardinal Ratzinger in Behold the Pierced One.