Many Christian denominations classify the Eucharist or Communion as a sacrament. Some others prefer to call it an ordinance, viewing it not as a specific channel of divine grace but as an expression of faith and of obedience to Christ.
Most Christians, even those who deny that there is any real change in the elements used, recognize a special presence of Christ in this rite, though they differ about exactly how, where, and when Christ is present.
Some Christian Denominations teach that the consecrated elements truly become the body and blood of Jesus Christ. Transubstantiation is the metaphysical explanation given by Roman Catholics as to how this transformation occurs.
Other denominations believe that the body and blood of Jesus are present "in, with and under" the forms of bread and wine, a concept known as the sacramental union. Some Christians reject the concept of the real presence, believing that the Eucharist is only a memorial of the death of Christ.
Now Let's see what Bible says about it.
In (John 6:53-58)Jesus said to them, "I tell you the truth, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is real food and my blood is real drink. Whoever eats my flesh and drinks my blood remains in me, and I in him. Just as the living Father sent me and I live because of the Father, so the one who feeds on me will live because of me. This is the bread that came down from heaven. Your forefathers ate manna and died, but he who feeds on this bread will live forever."
The Jews knew that He was speaking literally. They said "How can this man give us his Flesh to eat?" On other occasions when our Lord spoke of Himself as a "door" or a "vine," nobody said, "How can this man be made of wood?" or "How can this man be a plant?" They recognized these as metaphors.
But when Jesus insisted, "Unless you eat the Flesh of the Son of man and drink His Blood, you have no life in you; he who eats My Flesh and drinks My Blood has eternal life." The Jews who heard this said, "This is a hard saying; who can listen to it?"
The Bible teaches that Jesus allowed many of his disciples to abandon Him because they were rejecting the idea of eating his flesh and drinking his blood!!!
We see In John 6-60: that Many therefore of his disciples, when they had heard this, said, this is an hard saying; who can hear it? From that time many of his disciples went back, and walked no more with him. Jesus assured us, "He who eats my flesh and drinks my blood abides in me, and I in him."
The faith of the Church concerning the real presence of Jesus in the Eucharist under the appearances of bread and wine is traced back to the words of Jesus himself as recorded in the gospel of Saint John. The way in which Jesus is present in the Eucharist cannot be explained in physical terms because it transcends the ordinary necessities of space and measurement.
It is a supernatural mystery that the person who becomes fully present in bread and wine is the same Risen Savior who is seated at the right hand of the Father. In becoming present sacramentally, Christ's condition does not change. He does not have to leave heaven to become present on earth. Since we are constituted God's family -- God's people -- his Church -- precisely by our participation in the Eucharist, we cannot grow into Christ's new body as a healthy and full member without sharing in the Eucharist.
