The holy Eucharist completes Christian initiation. Those who have been raised to the dignity of the royal priesthood by Baptism and configured more deeply to Christ by Confirmation participate with the whole community in the Lord's own sacrifice by means of the Eucharist.
"At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice of his Body and Blood. This he did in order to perpetuate the sacrifice of the cross throughout the ages until he should come again, and so to entrust to his beloved Spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a Paschal banquet in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us."
The Eucharist is "the source and summit of the Christian life." "The other sacraments, and indeed all ecclesiastical ministries and works of the apostolate, are bound up with the Eucharist and are oriented toward it. For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself, our Pasch." (CCC 1322 - 1324)
Only validly ordained priests and bishops may consecrate the bread and wine, bringing about the transubstantiation of the bread and wine into the body and blood of Christ.
Only fully prepared Catholics may receive Holy Communion. A person is said to be fully prepared if they have been validly baptized, have confessed all mortal sins through the sacrament of Reconciliation and have fasted for at least one full hour prior to receiving.
Effects of the sacrament
Holy Communion augments our union with Christ. The principal fruit of receiving the Eucharist in Holy Communion is an intimate union with Christ Jesus. Indeed, the Lord said: "He who eats my flesh and drinks my blood abides in me, and I in him." Life in Christ has its foundation in the Eucharistic banquet: "As the living Father sent me, and I live because of the Father, so he who eats me will live because of me."
Holy Communion separates us from sin. The body of Christ we receive in Holy Communion is "given up for us," and the blood we drink "shed for the many for the forgiveness of sins." For this reason the Eucharist cannot unite us to Christ without at the same time cleansing us from past sins and preserving us from future sins.
The unity of the Mystical Body: the Eucharist makes the Church. Those who receive the Eucharist are united more closely to Christ. Through it Christ unites them to all the faithful in one body - the Church. Communion renews, strengthens, and deepens this incorporation into the Church, already achieved by Baptism. In Baptism we have been called to form but one body. The Eucharist fulfills this call: "The cup of blessing which we bless, is it not a participation in the blood of Christ? The bread which we break, is it not a participation in the body of Christ? Because there is one bread, we who are many are one body, for we all partake of the one bread:"
The Eucharist commits us to the poor. To receive in truth the Body and Blood of Christ given up for us, we must recognize Christ in the poorest, his brethren:
You have tasted the Blood of the Lord, yet you do not recognize your brother,. . . . You dishonor this table when you do not judge worthy of sharing your food someone judged worthy to take part in this meal. . . . God freed you from all your sins and invited you here, but you have not become more merciful.
The Eucharist and the unity of Christians. Before the greatness of this mystery St. Augustine exclaims, "O sacrament of devotion! O sign of unity! O bond of charity!4 The more painful the experience of the divisions in the Church which break the common participation in the table of the Lord, the more urgent are our prayers to the Lord that the time of complete unity among all who believe in him may return. (CCC 1391 - 1401)