The Eucharist, also known as Holy Communion, is the sacrament in which we receive the Body and Blood of Christ. We believe that Christ is actually present in the bread and wine that have been consecrated at Mass.
The origins of the Eucharist are in the Jewish Passover which commemorates Israel's deliverance from slavery by God. When Jesus celebrated Passover at his last supper with his apostles, he blessed, broke and shared the bread and wine, declaring that it was His body and blood. He promised he would be with them whenever they did the same in memory of him.
The Mass is the new Passover, with Jesus offering His own body and blood so that we might be free.
"While they were eating, Jesus took bread, said the blessing, broke it, and
giving it to his disciples said, 'Take and eat; this is my body.' Then he took a
cup, gave thanks, and gave it to them, saying, 'Drink from it, all of you, for
this is my blood of the covenant, which will be shed on behalf of many for the forgiveness of sins.'"