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. (CCC 1413)
The New Covenant
I am the living bread that came down from heaven; whoever eats this bread will live forever;…Whoever eats my flesh and drinks my blood has eternal life and…remains in me and I in him. (John 6:51, 54, 56)
In the gospels we read that the Eucharist was instituted at the Last Supper. This is the fulfillment of the covenants in the Hebrew Scriptures. In the Last Supper narratives, Jesus took, broke and gave bread and wine to his disciples. In the blessing of the cup of wine, Jesus calls it “the blood of the covenant” (Matthew and Mark) and the “new covenant in my blood” (Luke).
This reminds us of the blood ritual with which the covenant was ratified at Sinai (Ex 24) — the sprinkled the blood of sacrificed animals united God and Israel in one relationship, so now the shed blood of Jesus on the cross is the bond of union between new covenant partners — God the Father, Jesus and the Christian Church. Through Jesus’ sacrifice, all the baptized are in relationship with God.
The Catechism teaches that all Catholics who have received their First Holy Communion are welcome to receive Eucharist at Mass unless sin a state of mortal sin.
Anyone who desires to receive Christ in Eucharistic communion must be in the state of grace. Anyone aware of having sinned mortally must not receive communion without having received absolution in the sacrament of penance. (CCC 1415)
The Church warmly recommends that the faithful receive Holy Communion when they participate in the celebration of the Eucharist; she obliges them to do so at least once a year. (CCC 1417)
Receiving the Eucharist changes us. It signifies and effects the unity of the community and serves to strengthen the Body of Christ.