From YOUCAT, fact 208:
208: What is Holy Eucharist?
Holy Eucharist is the SACRAMENT in which Jesus Christ gives his Body and Blood – himself – for us, so that we too might give ourselves to him in love and be united with him in Holy COMMUNION. In this way we are joined with the one Body of Christ, the CHURCH.
After Baptism and CONFIRMATION, the Eucharist is the third sacrament of initiation of the Catholic Church. The Eucharist is the mysterious center of all these sacraments, because the historic sacrifice of Jesus on the Cross is made present during the words of consecration in a hidden, unbloody manner. Thus the celebration of the Eucharist is “the source and summit of the Christian life” (Second Vatican Council, Lumen gentium [LG], 11). Everything aims at this; besides this there is nothing greater that one could attain. When we eat the broken Bread, we unite ourselves with the love of Jesus, who gave his body for us on the wood of the Cross; when we drink from the chalice, we unite ourselves with him who even poured out his blood out of love for us. We did not invent this ritual. Jesus himself celebrated the Last Supper with his disciples and therein anticipated his death; he gave himself to his disciples under the signs of bread and wine and commanded them from then on, even after his death, to celebrate the EUCHARIST. “Do this in remembrance of me” (1 Cor 11:24).