The Eucharist (The Sacrifice of the Mass) is the most important act of worship, the most important prayer that we human beings have. It is not an act of worship that was devised by ordinary human beings but it is the act of worship that was given to us by Jesus, the divine Son of God.
It encapsulates, makes present for us, the unique and total act of worship and love that Jesus, the divine incarnate Son of God, made to his heavenly Father on our behalf by his death on the cross. It is the celebration of the new and everlasting covenant that Jesus established between God and humanity.
A few quotations from the Catechism of the Catholic Church:
1324. “The Eucharist is ‘the source and summit of the Christian life.‘ [LG 11.] ‘The other sacraments, and indeed all ecclesiastical ministries and works of the apostolate, are bound up with the Eucharist and are oriented toward it. For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself, our Pasch.’
1327. “...the Eucharist is the sum and summary of our faith: ‘Our way of thinking is attuned to the Eucharist, and the Eucharist in turn confirms our way of thinking.’ “
1359. “The Eucharist, the sacrament of our salvation accomplished by Christ on the cross, is also a sacrifice of praise in thanksgiving for the work of creation. In the Eucharistic sacrifice the whole of creation loved by God is presented to the Father through the death and the Resurrection of Christ. Through Christ the Church can offer the sacrifice of praise in thanksgiving for all that God has made good, beautiful, and just in creation and in humanity.”
Important to our understanding of the Eucharist (the Mass) is that it is a communal celebration, the act of worship given by Jesus to the community of his disciples, the Church. So our participating in the Mass and our receiving of the Eucharist at Communion is not a type of personal private devotion. (As are, for example: private prayer after the Mass, a visit to a church and spending some time before the Blessed Sacrament, the recitation of the Rosary, making a novena, praying the Divine Mercy chaplet, visiting Lourdes….) Our coming forward to receive the Eucharist at Communion is an integral part of our communal celebration of the Sacrifice of the Mass. To appreciate the background for this communal aspect of our receiving Communion we can consider that in ancient Israel the individuals who were making an offering to God in the Temple would eat some of what is offered as a communal participation in the sacrifice. Similarly our reception of the consecrated bread and wine is the expression of our communal acceptance and participation in the sacrifice that Jesus has made on the cross on our behalf. This is what is being expressed when going forward to receive the Eucharist from the priest or the Eucharistic Minister. We are reminded that this consecrated bread is now truly “The Body of Christ” (not just a piece of bread) to which we publicly reply “Amen” i.e. “Yes, I believe this to be true”. (Because our reception of the Eucharist is part of our communal celebration all are expected to adopt the same general approach used by the community in the service e.g. the individual receives the consecrated bread standing and not kneeling. It is not an occasion for making myself stand out. The focus is on Jesus and not on myself.)
One of the very earliest descriptions of the Eucharist is found in the first apology in defence of the Christians by Saint Justin, martyr. (The word “apology” as used here means a description that is written to explain to pagans what Christians do when they meet for their worship). As you read Justin’s description of the Eucharist as celebrated by the Christian community of his day, notice the similarities to our present celebration of the Eucharist.
The celebration of the Eucharist (Justin Martyr cir. 150AD)
No one may share the Eucharist with us unless he believes that what we teach is true, unless he is washed in the regenerating waters of baptism for the remission of his sins, and unless he lives in accordance with the principles given us by Christ.
We do not consume the eucharistic bread and wine as if it were ordinary food and drink, for we have been taught that as Jesus Christ our Saviour became a man of flesh and blood by the power of the Word of God, so also the food that our flesh and blood assimilates for its nourishment becomes the flesh and blood of the incarnate Jesus by the power of his own words contained in the prayer of thanksgiving.
The apostles, in their recollections, which are called gospels, handed down to us what Jesus commanded them to do. They tell us that he took bread, gave thanks and said: Do this in memory of me. This is my body. In the same way he took the cup, he gave thanks and said: This is my blood. The Lord gave this command to them alone. Ever since then we have constantly reminded one another of these things. The rich among us help the poor and we are always united. For all that we receive we praise the Creator of the universe through his Son Jesus Christ and through the Holy Spirit.
On Sunday we have a common assembly of all our members, whether they live in the city or the outlying districts. The recollections of the apostles or the writings of the prophets are read, as long as there is time. When the reader has finished, the president of the assembly speaks to us; he urges everyone to imitate the examples of virtue we have heard in the readings. Then we all stand up together and pray.
On the conclusion of our prayer, bread and wine and water are brought forward. The president offers prayers and gives thanks to the best of his ability, and the people give assent by saying, “Amen.” The eucharist is distributed, everyone present communicates, and the deacons take it to those who are absent.
The wealthy, if they wish, may make a contribution, and they themselves decide the amount. The collection is placed in the custody of the president, who uses it to help the orphans and widows and all who for any reason are in distress, whether because they are sick, in prison, or away from home. In a word, he takes care of all who are in need.
We hold our common assembly on Sunday because it is the first day of the week, the day on which God put darkness and chaos to flight and created the world, and because on that same day our saviour Jesus Christ rose from the dead. For he was crucified on Friday and on Sunday he appeared to his apostles and disciples and taught them the things that we have passed on for your consideration.
Quotations from chapter six of the Gospel according to John
35 Jesus said to them, “I am the bread of life; whoever comes to me will never hunger, and whoever believes in me will never thirst.
51 I am the living bread that came down from heaven; whoever eats this bread will live forever; and the bread that I will give is my flesh for the life of the world.”
53 Jesus said to them, “Amen, amen, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you do not have life within you. 54 Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day. 55 For my flesh is true food, and my blood is true drink. 56 Whoever eats my flesh and drinks my blood remains in me and I in him. 57 Just as the living Father sent me and I have life because of the Father, so also the one who feeds on me will have life because of me. 58 This is the bread that came down from heaven. … whoever eats this bread will live forever.”