Jesus said: “I am the living bread that came down from heaven; if any one eats of this bread, he will live forever; …he who eats my flesh and drinks my blood has eternal life and … abides in me, and I in him.” (John 6:51, 54, 56).
One of the seven sacraments of the Church, indeed the greatest of the sacraments, described by the Church in this way: “The Most Holy Eucharist is the most august sacrament, in which Christ the Lord himself is contained, offered and received, and by which the Church constantly lives and grows. The Eucharistic Sacrifice, the memorial of the death and resurrection of the Lord, in which the sacrifice of the cross is perpetuated over the centuries, is the summit and the source of all Christian worship and life; it signifies and affects the unity of the people of God and achieves the building up of the Body of Christ. The other sacraments and all the ecclesiastical works of the apostolate are closely related to the Holy Eucharist and are directed to it.” — Canon Law 897.
Although the Eucharist is one sacrament, there are three essential aspects to which the Church points: (1) sacrifice; (2) communion; (3) Real Presence of Christ.
The Church calls the faithful to respond in faith to these three aspects of the Eucharist: “The faithful are to hold the Eucharist in highest honor, taking part in the celebration of the Most August Sacrifice, receiving the sacrament devoutly and frequently, and worshiping it with supreme adoration….” — Canon Law 898.