This is the most venerated of all Christian sacraments, and also the one over which there has been most misunderstanding and argument through the centuries. As baptism provides for our entry in to the Christian community, so the Eucharist provides the focus for our spiritual nourishment for our Christian life and journey. The Eucharist has such richness of content and breadth of symbolism that it is difficult to speak adequately of it. This richness is reflected in the differing names associated with this sacrament. It is the Eucharist, or thanksgiving; it is the Mass, and whatever this may have meant originally, it has come to denote sacrifice; it is the Holy Communion, in which the worshipper is united with God through Christ, and also with each other in the body of Christ; it is the Lord's Supper. And this title reminds us of the dominical connection of the sacrament, and that in it we receive from Christ the grace that sustains and nourishes the Christian life. As a sacrament the Eucharist makes use of the outward, visible elements of bread and wine. It enshrines as its core and inner meaning a making present of Christ and his grace. It incorporates the recipient into the body of Christ and conforms his existence to the pattern of Christ.
Two aspects of the Eucharist which have been at the centre of disputes are those of Eucharistic sacrifice and 'real presence'. Obviously the Eucharist is not a literal repetition of Christ's sacrifice which took place once and for all on the first Maundy Thursday in the Upper Room. It could more accurately be thought of in terms of a re-presentation of Christ's sacrifice within the context of the Christian community, so that the self-giving which he manifested, and which is the very essence of God himself, realizes itself now in the community, so that this community is being conformed to Christ - with the aim that eventually all humanity will be so conformed. There are two points at which the Eucharistic rite touches on the point of sacrifice. First there is the offering of bread and wine before the consecration - which we call offertory. Secondly the offering of these elements after consecration when they have been made the vehicles that re-present the body and blood of Christ - which we call oblation.
The offering of bread and wine before is done by everyone. The elements are brought to the altar, the products of human labour and the means of human sustenance. Our offerings of money of course are representative of this and are our sacrifice or giving of ourselves.
The oblation is done by the priest alone, for he is acting in Christ's place, and thus it is Christ who makes the oblation. In the Eucharist too he is still both priest and victim. It is a saving happening. In the breaking and outpouring of the consecrated elements and their reception by the communicants Christ is offering in union with himself the congregation and indeed, ideally, all humanity. The lives brought to the altar at the offertory are incorporated into Christ, so that they share in his sacrifice, are conformed to his image, are sanctified by his Spirit, and so brought to their fulfillment in God.
The Real Presence is an extension of the above ideas. We call say that Christ is really present throughout the universe, and yet here this presence is focused in such a way that he is truly available to us, of course in a spiritual sense. This focus is concentrated on the consecrated elements, which thus in some real way become Christ himself. The doctrine of transubstantiation of St. Thomas Aquinas was an attempt to explain this, which to Anglicans and the Orthodox is unexplainable. The Anglican way is to leave a sense of mystery. However this belief does remain faithful to the words of institution -This is my Body: This is my Blood.