The Eucharist (Grk: Thanksgiving) is the central Sacrament of the largest Christian churches. It is served at every Mass of the Roman Catholic and Anglican churches, and every Divine Liturgy of the Orthodox Church.
The rite itself varies depending on which church and which rite is being followed but this has been the case since the beginning of the Church. In its most basic an unadorned form, the eucharist is very simple. The 1st century A.D. manual called the Didache gives the following instructions:
Chapter 9. The Eucharist. Now concerning the Eucharist, give thanks this way. First, concerning the cup:
We thank thee, our Father, for the holy vine of David Thy servant, which You madest known to us through Jesus Thy Servant; to Thee be the glory for ever..
And concerning the broken bread: We thank Thee, our Father, for the life and knowledge which You madest known to us through Jesus Thy Servant; to Thee be the glory for ever. Even as this broken bread was scattered over the hills, and was gathered together and became one, so let Thy Church be gathered together from the ends of the earth into Thy kingdom; for Thine is the glory and the power through Jesus Christ for ever.. But let no one eat or drink of your Eucharist, unless they have been baptized into the name of the Lord; for concerning this also the Lord has said, "Give not that which is holy to the dogs."
Chapter 10. Prayer after Communion. But after you are filled, give thanks this way: We thank Thee, holy Father, for Thy holy name which You didst cause to tabernacle in our hearts, and for the knowledge and faith and immortality, which You modest known to us through Jesus Thy Servant; to Thee be the glory for ever. Thou, Master almighty, didst create all things for Thy name's sake; You gavest food and drink to men for enjoyment, that they might give thanks to Thee; but to us You didst freely give spiritual food and drink and life eternal through Thy Servant. Before all things we thank Thee that You are mighty; to Thee be the glory for ever. Remember, Lord, Thy Church, to deliver it from all evil and to make it perfect in Thy love, and gather it from the four winds, sanctified for Thy kingdom which Thou have prepared for it; for Thine is the power and the glory for ever. Let grace come, and let this world pass away. Hosanna to the God (Son) of David! If any one is holy, let him come; if any one is not so, let him repent. Maranatha. Amen. But permit the prophets to make Thanksgiving as much as they desire.
Commonly called in Protestant churches "the Lord's Supper" or Communion, this part of the Christian worship service centering on the "remembering of Christ" over the bread and the wine, as He commanded, is known in Orthodox and Catholic (Also Anglican) churches as the Eucharist. "Eucharist" coming from the Greek word meaning "giving thanks" is so called because the "centerpiece" of intent is being grateful to God for His gift of His Son Jesus and Jesus' sacrificial death on the cross for our sins. It also derives its name from the 3rd cup of wine drunk immediately after the Passover Seder dinner, in which Jesus instituted the Eucharist - called "the cup of Thanksgiving"..
The following is the basic eucharistic theology of all Catholic and Orthodox churces, East or West, Latin, Greek, or Aramaic.
The foreservice of the Eucharist, is Scripture readings according to a lectionary of Scripture. This practice came into the Church through the Synagogual reading of the Law of Moses (Torah) and the Prophets (Haftorah). Starting from the early Church, the "memoires of the Apostles', the Gospels, were added with the additions, as in the synagogue, of the recitation from the Psalms. In the early Church, but no longer, those who have not yet been baptized left the Church, and the Eucharist was celebrated by the baptized believers.
The pattern of the service follows certain "cues" preserved in the Gospels and elsewhere that provide a key to understanding those portions of Scriptures. The pattern is fourfold:
1. TAKING the bread and the wine (the produce of our labor and hence, often accompanied with the "Offerings" of our tithes and donations). In the Orthodox churches there is a prayerfull Preparation of the bread and wine before being brought to the altar.
2. BLESSING the bread and wine, understood, as in Judaism, as a blessing of the God who has given them to us. The blessing of God over the bread in Judaism sanctifies the bread taking it out of normal use, or, alternatively, bringing the "secular" into the arena of the divine. This Blessing is known as the Thanksgiving prayer proper.
3. BREAKING or "Fraction" (meaning breaking) The Fraction both signifies that Jesus' body was broken for us on the hill of Calvary and it is the start of the breaking and giving to all the people in the congregation - as Jesus did on the hills of Galilee
4. the COMMUNION (that is, the distribution of the blessed Bread and Wine to the congregation). The term "Communion", here is reserved for this particular part of the service. In the Roman Catholic Church the blessed bread is usually unleavened, as was the Matzah of the Passover, perpetuating the link with Jewish practice, and for convenience, is usually small wafers. In the Orthodox Church, the bread is a loaf of bread (intermingled with the wine in the Chalice) following the symbolism of the Apostle Paul that as the loave is one, so we who partake are one.
These Churches consider their Eucharists not only as a fullfilment and continuation of what the Lord did and commanded at the Last Supper, but also continuation and fulfillment of those events in the Gospels that portray this fourfold pattern and mentioning it (when there is no need to) sometimes all four together. The Lord takes the bread (also the fish*), He blesses looking up to heaven, He breakes the bread (this is needed in order to put into the hands of the disciples who distribute to the people, but there is no need to mention it except for the link seen connecting the Lord's miracle in th4 Gospels with the Eucharist). And the miracle takes place. Also the Lord is known in the "breaking" of the bread at Emmaus. This shows that the people of New Testament formation times, understood that their actual practice of the Eucharist was an extension of the miracle supply that Jesus gave the people when He was earth. and that is why they held interest in these events causing the need to preserve them in the recounting of the events in the Gospels. In similiar ways were their experiences at Church with the events related to Christs provision in the Gospels. .
In the Eucharist then, the priest takes the bread, and he blesses. These churches understand that here the priest (who also gives the Word and pastors the people) stands in the place of Christ. That is, it is not the table of the priest or even of the people, it is the table of Christ. It is Christ who streches out his hands to invite the people to the banquet, and Christ Himself is the host of the banquet. This is the mind-set of the priest who is called the Celebrant. Here is to be noted a double understanding of the priest. He represents Christ behind the altar to the people, but in taking the bread and wine,and in his prayers, he represents the people to the Lord. In this sense he has a double capacity just like the priest, the "Cohen" of the Old Testament. But the priest is not of the order of the Aaronic priesthood; Christ is understood to be that. (the New Testament word "Priest" is but the linguistic corruption from the Greek word Presbyter, meaning "elder" - which is a direct derivation from the Hebrew Zaqen, also meaning "elder")
The Priest then makes the Eucharistic prayer. Here he is representing all the people assembled. This is the Thanksgiving proper. Thanksgiving is made for Creation and sustenance and protection but the core of the thanksgiving, in all the liturgies, is for the giving of the Father of His Son, and for the willing sacrifice of Himself that Jesus performed, and then the prayer of thanksgiving settles on the words of Jesus which Jesus said when He instituted the Eucharist at the last supper. That is, Jesus commanded that something be done, "Do this!...", and it is done in the Churches and it is accompanied by Jesus' own words as given in the Gospels."This is my body which is given for you...This is the cup of my blood, the blood of the New Covenent which is poured out for you, and for many..." This recitation in prayer is called the Words of Institution, and it one of the two "essentials" of the Eucharist. The second essential is the prayer of calling for the sanctifying Holy Spirit, the Invocation, upon both the elements of Bread and Wine that it become for the people of God, the Body and Blood of the Lord, and upon the people that they will be made worthy and make a "furitful" communion.
What takes place at the Eucharist is understood to be two-fold, one. a complete sure line of development of Old Testament teachings and the other an understanding of the intent of the Gospels. The first of the two-fold: The bread and the wine, is not only to visualize the willing sacrifice of the Lord for the sins of the whole world, as is shared with most Protestant churches, but they are considered signs of the covenant, in Hebrew, Otot haBrit, and like the Signs of the Covenant in the Old Testament itself, they are primarily for the eyes of God. (This is a difference with most Protestant churches that understand the Lord's supper to be "pedagogic", that is, a reminder to the people of what Christ has done for us on the cross, and a call ffor evaluation of our lives in view of His great sacrifice on the cross). The people of the Lord are lifting up the signs of the Covenant commanded by God to heaven itself. Heaven (God) looks down and sees the signs, sees the faith of the people that are under the sign, sees their taking refuge in what the signs represent, and so they, the people are found safe under the wings of His grace and mercy. The signs of the New Covenant are thus analogous to the Old Covenant signs that God looked down upon - the blood of the lamb at the first Passover, which was placed by the people who believed, which was seen by the angel, and so the people taking refuge as God commanded, were spared; the circumcision of the Israelites at eight days, which Moses neglected to do for his own son, and was spared only because of the faithful love and determination of his wife who did the job for him; the rainbow in the skies, which, when God would look at, He would remember His promise to spare, and thus the earth would know no more destruction by water as in the days of Noah. These are all echoes in the Jewish "Remembrance " prayers from the time of Jesus and thus the natural setting for the expression of the Eucharist is provided. But aside from the setting up of the sign of the New Covenant, there is the other of the two-fold understandings of what takes place at the Eucharist:
Taking their cues from the sixth chapter of the Gospel of John where Jesus speaks about eating His body and drinking His blood, and understanding that this is meant Eucharistically, that is, to be understood from the meaning and practice of the Eucharist as instituted by Jesus at the Last Supper (no need therefore for the Gospel of John to include the recounting of the Last Supper), Orthodox and Catholic Churches (as well as Anglican and Lutheran) believe that the life of Christ in His body and blood are presented to the people at the time of communion. How this is done differs in the understanding of Catholic from Orthodox, but that it is done, is a shared understanding. The Roman Catholic church, influenced by Aristotle through the writings of Thomas Aquinus, has adopted the understanding and belief that there is nothing any longer of the substance of bread and wine; that the substance of bread and wine are no longer there, though the "accidents", taste, smell, feel, of bread and wine remain (Transubstantiation). The Orthodox believe otherwise, understanding that the words of Christ This is my body and This is my blood, signify what is said without explanation. What both Churches do share, is that any offering is acceptable to God, even the offering of Christ Himself according to the book of Hebrews, only through the Holy Spirit, and that what is of the earth is earthly and only that which is of the Spirit, is spiritual - and thus the Invocation.
The various Orthodox and Catholic Churches do have other differences as well as other similarities, but the above is the basics of their shared Eucharist.
Passover Seder and its connection to the Lord's Supper
See , (Document: Liturgy of the Eucharist, annotated) for example of how the above Eucharistic basics may be adapted by Apostolic succession church for modern usage and worship service.