My brothers and sisters, pray for me, a sinner. Always remember the following canons, because to partake of the Eucharist while in a state of mortal sin is itself a mortal sin [Summa Theologica III, q. 80, art. 4, corp.]; the good fruits described below do not reach those who partake unworthily:
Can. 915 Those who have been excommunicated or interdicted after the imposition or declaration of the penalty and others obstinately persevering in manifest grave sin are not to be admitted to Holy Communion.The following comes from the Catechism of the Catholic Church §1391-1398:
Can. 916 A person who is conscious of grave sin is not to celebrate Mass or receive the Body of the Lord without previous sacramental Confession unless there is a grave reason and there is no opportunity to confess; in this case the person is to remember the obligation to make an act of perfect contrition which includes the resolution of confessing as soon as possible.
1391 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."223 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."224
223 Jn 6:56.
224 Jn 6:57.
On the feasts of the Lord, when the faithful receive the Body of the Son, they proclaim to one another the Good News that the first fruits of life have been given, as when the angel said to Mary Magdalene, "Christ is risen!" Now too are life and resurrection conferred on whoever receives Christ.225
225 Fanqith, Syriac Office of Antioch, Vol. 1, Commun., 237 a-b.
1392 What material food produces in our bodily life, Holy Communion wonderfully achieves in our spiritual life. Communion with the Flesh of the risen Christ, a Flesh "given life and giving life through the Holy Spirit,"226 preserves, increases, and renews the life of grace received at Baptism. This growth in Christian life needs the nourishment of Eucharistic Communion, the bread for our pilgrimage until the moment of death, when it will be given to us as viaticum.
226 PO 5.
1393 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:
For as often as we eat this bread and drink the cup, we proclaim the death of the Lord. If we proclaim the Lord's death, we proclaim the forgiveness of sins. If, as often as His Blood is poured out, it is poured for the forgiveness of sins, I should always receive it, so that it may always forgive my sins. Because I always sin, I should always have a remedy.227227 St. Ambrose, De Sacr. 4, 6, 28: PL 16, 446; cf. 1 Cor 11:26.
1394 As bodily nourishment restores lost strength, so the Eucharist strengthens our charity, which tends to be weakened in daily life; and this living charity wipes away venial sins.228 By giving Himself to us Christ revives our love and enables us to break our disordered attachments to creatures and root ourselves in Him:
Since Christ died for us out of love, when we celebrate the memorial of His death at the moment of sacrifice we ask that love may be granted to us by the coming of the Holy Spirit. We humbly pray that in the strength of this love by which Christ willed to die for us, we, by receiving the gift of the Holy Spirit, may be able to consider the world as crucified for us, and to be ourselves as crucified to the world. ... Having received the gift of love, let us die to sin and live for God.229228 Cf. Council of Trent (1551): DS 1638.
229 St. Fulgentius of Ruspe, Contra Fab. 28, 16-19: CCL 19A, 813-814.
1395 By the same charity that it enkindles in us, the Eucharist preserves us from future mortal sins. The more we share the life of Christ and progress in His friendship, the more difficult it is to break away from Him by mortal sin. The Eucharist is not ordered to the forgiveness of mortal sins - that is proper to the sacrament of Reconciliation. The Eucharist is properly the sacrament of those who are in full communion with the Church.
1396 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.230 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:"231
If you are the body and members of Christ, then it is your sacrament that is placed on the table of the Lord; it is your sacrament that you receive. To that which you are you respond "Amen" ("yes, it is true!") and by responding to it you assent to it. For you hear the words, "the Body of Christ" and respond "Amen." Be then a member of the Body of Christ that your Amen may be true.232230 Cf. 1 Cor 12:13.
231 1 Cor 10:16-17.
232 St. Augustine, Sermo 272: PL 38, 1247.
1397 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.233233 St. John Chrysostom, Hom. in 1 Cor. 27, 4: PG 61, 229-230; cf. Mt 25:40.
1398 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!"234 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.
234 St. Augustine, In Jo. ev. 26, 13: PL 35, 1613; cf. SC 47.