How to explain the Catholic belief that during the celebration of Holy Eucharist the bread (the host) is changed into the “Body of Christ”? Isn’t the host made of normal flour of wheat?
The host is composed of flour and water, and if it were submitted to analysis at a molecular level, one would surely find water and flour. After all, when the priest is preparing the gift of bread he prays, “Blessed are you, Lord, God of all creation. Through your goodness we have this bread to offer, which earth has given and human hands have made. It will become for us the bread of life.” This is both a connexion to the earlier Jewish prayer of blessing over a meal, as well as a recognition that what is being offered at the Eucharist is bread, and that what is hoped is that God will accept it as sacrifice. Human beings are not making anything, instead it is all done in the recognition of human and creaturely frailty and relying entirely on God himself. Christians believe that Eucharist is the work of God, that they participate in it as God's gift.
The experience of the Resurrection from the Dead of Jesus Christ was a confusing event for the early followers of his Way, even a terrifying one. They did not know what to make of it, how to trust it, or even what was happening. “While they were talking about this, Jesus himself stood among them and said to them, 'Peace be with you.' They were startled and terrified, and thought that they were seeing a ghost. He said to them, 'Why are you frightened, and why do doubts arise in your hearts?'" (Luke 24:36-38) This fear is fully understandable, because we believe that these events reflect the work of God and not of humankind. Before Jesus Christ offered himself to death on the Cross, he had celebrated what seemed like a normal feast meal in the Jewish tradition and culture. (Matthew 26:26-30; Mark 12:22-24; Luke 22:14-23) He blessed bread, shared bread, and celebrated God’s liberation of his people, with his disciples who were his friends. He also took a cup of wine, and shared it with them, proclaiming it to be his blood. But he also said while doing it, “Do this in memory of me.” (Luke 22:19) In offering his body and his blood in the Eucharist, Jesus is offering us the fullness of relationship with God. This was an added dimension that raised this simple shared meal into what Christians understand to be the Eucharist, what we celebrate in thanksgiving when we gather together to worship. (1 Cor 11:23-26)
After his Resurrection, Jesus Christ appeared to some of his despondent disciples who were walking on the Road to Emmaus, close to Jerusalem. (Luke 24:13-35) At first, and it seems for some while, these disciples did not recognise him, but only when they sat down together for a meal and then Jesus Christ took bread, broke it, and blessed it, and then gave it to them and they then immediately recognised him in the “breaking of the bread.” (Luke 24:35) This is to say, that for us the Eucharist is something celebrated by humankind with created materials from nature, but that the actual event of Eucharist is not produced by humankind, but rather it is Jesus himself gifting us communion. Indeed, we are in community together as a "church" it is precisely because it is the community that Jesus gathers. He is our guarantee to our relationship with God as Father, and the bond that unites us altogether. In this way, the body and blood offered in communion by Jesus to God the Father on our behalf says a lot about what precisely this community is. Hence, when we receive the Eucharist, we say that we are “communicating.”
At the last supper, it was Jesus who gifted the meal to his disciples and told them to do this in memory of him. This sense of “memory” does not mean to recall something; rather it captures the re-membering of something. It is for something to be present. The Greek word is anamnesis. This expresses the Semitic root from Hebrew of “z-k-r” or in Aramaic “d-k-r”, which of course reminds us of the Arabic “zikr” What Jesus gifted the disciples at that meal was communion, to have the gift of participating in what God wills for all creation and what we understand to be either vocation of living in accordance with God's will.
We believe that all of Creation finds its proper fulfilment by being in communion, or relationship, with God. All Creation is meant to glorify God and proclaim God's glory to others. For us, Jesus is the most perfect correspondence to the Heavenly Father, the ‹Son›, because he is most in communion with God , he is most in relationship to God. Jesus himself gifted this communion. He transformed the simple bread so that it would be itself like him, in terms of being what it is supposed to truly be, something that is in communion with God and offers this communion to others. That is to say that the bread physically remains flour and water, but for our communion I t is the body of Christ, proclaiming the Glory of God and the true purpose of Creation.