The Eucharist is the most special sacrament, in which Christ 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 source of all Christian life and worship; it signifies and affects the unity of the people of God and achieves the building up of the Body of Christ.
As children reach the age of reason, generally around age seven, the Church extends to them an invitation to celebrate the sacrament of Eucharist. The initiation into the Christian community that took place at baptism is further extended by inviting children to enter fully into the heart of Christian faith through participation in the Eucharist.
The Eucharist is the sacrament by which Catholics receive the Body and Blood of Jesus Christ. For Catholics, this is the most treasured gift given to the Church by the Lord at the Last Supper. In receiving the Eucharist, we are nourished by the Lord. The bread and wine used in the Mass are transformed in all but appearance into the Body and Blood of Christ.
The Catechism of the Catholic Church on the Eucharist (1406-1419):
Jesus said: “I am the living bread that came down from heaven; if any one eats of this bread, he will live for ever; … he who eats my flesh and drinks my blood has eternal life and … abides in me, and I in him” (Jn 6:51, 54, 56).
The Eucharist is the heart and the summit of the Church’s life, for in it Christ associates his Church and all her members with his sacrifice of praise and thanksgiving offered once for all on the cross to his Father; by this sacrifice he pours out the graces of salvation on his Body which is the Church.
The Eucharistic celebration always includes: the proclamation of the Word of God; thanksgiving to God the Father for all his benefits, above all the gift of his Son; the consecration of bread and wine; and participation in the liturgical banquet by receiving the Lord’s body and blood. These elements constitute one single act of worship.
The Eucharist is the memorial of Christ’s Passover, that is, of the work of salvation accomplished by the life, death, and resurrection of Christ, a work made present by the liturgical action.
It is Christ himself, the eternal high priest of the New Covenant who, acting through the ministry of the priests, offers the Eucharistic sacrifice. And it is the same Christ, really present under the species of bread and wine, who is the offering of the Eucharistic sacrifice.
Only validly ordained priests can preside at the Eucharist and consecrate the bread and the wine so that they become the Body and Blood of the Lord.
The essential signs of the Eucharistic sacrament are wheat bread and grape wine, on which the blessing of the Holy Spirit is invoked and the priest pronounces the words of consecration spoken by Jesus during the Last Supper: “This is my body which will be given up for you…. This is the cup of my blood….”
By the consecration the transubstantiation of the bread and wine into the Body and Blood of Christ is brought about. Under the consecrated species of bread and wine Christ himself, living and glorious, is present in a true, real, and substantial manner: his Body and his Blood, with his soul and his divinity (cf. Council of Trent: DS 1640; 1651).
As sacrifice, the Eucharist is also offered in reparation for the sins of the living and the dead and to obtain spiritual or temporal benefits from God.