Jesus took a loaf of bread, and after blessing it he broke it,
gave it to the disciples, and said, “Take, eat; this is my body.” 
Then he took a cup, and after giving thanks he gave it to them,
saying, “Drink from it, all of you; for this is my blood of the covenant,
which is poured out for many for the forgiveness of sins.” 
~ Matthew 26:26-28

“At the heart of the Eucharistic celebration are the bread and wine that, by the words of Christ and the invocation of the Holy Spirit, become Christ's Body and Blood. The Eucharist is the “source and summit of the Christian life,” and the third sacrament of initiation.  "It is the culmination both of God's action sanctifying the world in Christ and of the worship men offer to Christ and through him to the Father in the Holy Spirit."

(Catechism of the Catholic Church, 1333,1324,1325)