The Sacrament of the Eucharist
"I am the living bread which came down from heaven;
if any one eats this bread, he will live forever;
and the bread which i shal give for the life of the world is My Flesh.
Unless you eat the Flesh of the Son of Man and drink His Blood,
you have no life in you;
he who eats My Flesh and drinks My Blood has eternal life."
Jn 6:51, 53
The Holy Eucharist is the greatest gift ever given to man. The second Sacrament of Initiation, it is the greatest of all the Sacraments since it is truly the living presence of Jesus Christ, Body and Blood, Soul and Divinity, which nourishes the Mystical Body with His very Flesh. That is why this Sacrament is called the Blessed Sacrament. It is more than just an outward sign, it is the very Person of Christ and the very pinnacle of our faith.
The Eucharistic miracle occurs each time the Holy Sacrifice of the Mass is offered on all Catholic altars throughout the entire world. During the Consecration, Christ, through the Priest, offers Himself as a sacrifice for us again. At that moment, all the events of Christ's life are unraveled before the eyes of the congregation. The newborn King again rests in the stable at Bethlehem, which is appropriately translated as "House of Grain," the promise of the Eucharist promised by Christ during His ministry is fulfilled, and the Sacrifice of the Lamb of God on Calvary is renewed for the remission of sins. That is why it is such a grave sin for one not to attend Mass on Sundays and Holy Days of Obligation. By denying oneself the nourishment of God, the soul dies spiritually just as the body would die physically of starvation if one refuses or is denied food.
By coming to us in the simple appearances of bread and wine, Christ desires to be united with us in the most intimate way. As Fr. Joseph T. Szolack of the Diocese of Camden says, "It is not so much us who consumes Him as it is He Who consumes us." On the part of the communicant, it is necessary for one who desires to receive Holy Communion to be in the state of grace, meaning the communicant is a practicing Catholic and free of all attachment to mortal sin.
Sacraments 101: Eucharist (How we receive)
Sophia SketchPad: The Eucharist
Sacraments 201: Eucharist (What we believe)
Bishop Barron on the Real Presence of Christ in the Eucharist