The eucharist is about the way we are with each other, about our unity. This is obvious from its shape, a ritual meal, an eating and drinking together, to say we share one life.
Now it is not just an ordinary ritual meal, but a sacramental ritual meal, because it expresses the mystery of our unity. It is plain that the eucharist is not a meal any more than baptism is taking a shower. It ought not to look like an occasion when hungry people come to eat and drink. It is a token meal, when something is said. The bread and wine are there for symbolism, not nourishment, though of course they wouldn't have their symbolism if they weren't food and drink.
A purely ritual meal in which all share a token portion of bread and wine is purely symbolic, a piece of language, a word. It is not because the eucharist is a sacrament that bread and wine become signs: they are already signs in a perfectly ordinary way. To see the eucharist as a sacrament is to see it as symbolic not just of our human friendship or of the human mystery within it, but of the unfathomable mystery within and beyond it, of community in the Spirit of God.
We cannot express this unity in the Spirit in the same signs with which we symbolise human friendship; they have to be transformed into a new language. We can attempt to express the depth of human relationships in human words, but they cannot adequately express our relationship in the Spirit. Only God can speak of God: to express this unity we need not just human speech but God's speech. That is what it is for the eucharist to be a sacrament: what on the face of it are human words deepen into God's Word, which speaks the unfathomable mystery of his love in which we share.
The eucharist is also the sacrament of the human body of Christ. The Word by which God's love is made present amongst us is not in the first place words, but a human being of flesh and blood, not an idea about God, but the enacted life-story of Jesus of Nazareth. When we say God's Word expresses our unity in the Spirit in the eucharist, we mean that language used for our love for each other is no longer just human words of bread and wine, but the divine Word-made-flesh, the real body and blood of Christ.
This is the difference between Catholic teaching and the idea that bread and wine are human symbols expressing what Christ does for us. Catholics say that this cannot be expressed except in God's language; it can only be spoken by God's speaking his Word, the bodily reality of Jesus. It is not just that our language is now used to speak of Christ, but Christ himself, the Word, is now our language: our words, symbolic bread and wine, have become Christ, the flesh and blood of God's Word.
So while to one without faith we seem to be dealing simply in human symbols, we know that that is only to look at appearances. In reality it is the body and blood of God's Word, his whole humanity, that is the sign of our unity in the Spirit. When we eat his body and drink his blood, we speak and hear God's Word telling of our divine friendship, just as when we share human food we speak a human word of human friendship.
Finally, the eucharist is the sacrament of a body broken and blood shed. Jesus' life-story was completed in his execution. His obedience to his mission to be truly human meant that we, the world, killed him. Because of the disunited world we have made, the Word takes flesh that is tortured and killed. The divine language and sacrament of our unity is Christ's body broken and blood shed.
This feast of friendship celebrates the cross. This friendship the world will hate and it belongs to those in solidarity with the victims of the world, and expects only suffering and death. The sacrament of love is also sacrament of death - Christ's death through which we come to a new life in the love which is the Holy Spirit, in which we shall live for eternity.