The Catholic Church has produced the Catechism of the Catholic Church to make clear the official teachings of the Church on important issues. The following excerpts give you parts of the official Catholic Church positions on Sacraments, Holy Communion, and sin.
Each paragraph of the catechism is numbered so that it can easily be found regardless of language, page size, etc of various published copies. Here the paragraph numbers are at the start of each quote.
1084 Christ now acts through the sacraments he instituted to communicate his grace. The sacraments are perceptible signs (words and actions) accessible to our human nature. By the action of Christ and the power of the Holy Spirit they make present efficaciously the grace that they signify.
1127 Celebrated worthily in faith, the sacraments confer the grace that they signify. They are efficacious because in them Christ himself is at work:…
1131 The sacraments are efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us. The visible rites by which the sacraments are celebrated signify and make present the graces proper to each sacrament. They bear fruit in those who receive them with the required dispositions.
1141 Mother Church earnestly desires that all the faithful should be led to that full, conscious, and active participation in liturgical celebrations which is demanded by the very nature of the liturgy,…
1129 ”Sacramental grace” is the grace of the Holy Spirit, given by Christ and proper to each sacrament. The Spirit heals and transforms those who receive him by conforming them to the Son of God.
1368 The lives of the faithful, their praise, sufferings, prayer, and work, are united with those of Christ and with his total offering, and so acquire a new value.
1098 The assembly should prepare itself to encounter its Lord and to become “a people well disposed.” The preparation of hearts is the joint work of the Holy Spirit and the assembly, especially of its ministers. The grace of the Holy Spirit seeks to awaken faith, conversion of heart, and adherence to the Father’s will. These dispositions are the precondition both for the reception of other graces conferred in the celebration itself and the fruits of new life which the celebration is intended to produce afterward.
1146 As a social being, man needs signs and symbols to communicate with others, through language, gestures, and actions. The same holds true for his relationship with God.
1124 The Church’s faith precedes the faith of the believer who is invited to adhere to it.
1123 They (the Sacraments) not only presuppose faith, but by words and objects they also nourish, strengthen, and express it.
1124 lex orandi, lex credendi … The law of prayer is the law of faith: the Church believes as she prays.
1128 ”the sacrament is not wrought by the righteousness of either the celebrant or the recipient, but by the power of God.”
1116 Sacraments are “powers that come forth” from the Body of Christ, which is ever-living and life-giving.
EUCHARIST / HOLY COMMUNION
1211 The Eucharist occupies a unique place as the “Sacrament of sacraments”: “all the other sacraments are ordered to it as to their end.”
1074 “The liturgy is the summit toward which the activity of the Church is directed; it is also the font from which all her power flows.”
1350 …Christ, who in his sacrifice, brings to perfection all human attempts to offer sacrifices.
1212 The faithful … receive in the Eucharist the food of eternal life.
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,” preserves, increases, and renews the life of grace received at Baptism. This growth in Christian life needs the nourishment of Eucharistic Communion,
1324 For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself
1331 Holy Communion,…by this sacrament we unite ourselves to Christ, who makes us sharers in his Body and Blood to form a single body.
1333 The signs of bread and wine become, in a way surpassing understanding, the Body and Blood of Christ; they continue also to signify the goodness of creation.
1391 The principal fruit of receiving … Holy Communion is an intimate union with Christ Jesus.
1104 Christian liturgy not only recalls the events that saved us but actualizes them, makes them present. The Paschal mystery of Christ is celebrated, not repeated.
1366 The Eucharist is thus a sacrifice because it re-presents (makes present) the sacrifice of the cross,… [he wanted] to leave to his beloved spouse the Church a visible sacrifice (as the nature of man demands) by which the bloody sacrifice which he was to accomplish once for all on the cross would be re-presented,
1085 His Paschal mystery is a real event that occurred in our history, but it is unique: all other historical events happen once, and then they pass away, swallowed up in the past. The Paschal mystery of Christ, by contrast, cannot remain only in the past, because by his death he destroyed death, and all that Christ is – all that he did and suffered for all men – participates in the divine eternity, and so transcends all times while being made present in them all. The event of the Cross and Resurrection abides and draws everything toward life.
1393 The Eucharist cannot unite us to Christ without at the same time cleansing us from past sins and preserving us from future sins:
1394 As bodily nourishment restores lost strength, so the Eucharist strengthens our charity … and this living charity wipes away venial sins. by giving himself to us Christ revives our love…
1472 …sin has a double consequence. Grave sin deprives us of communion with God and therefore makes us incapable of eternal life, the privation of which is called the “eternal punishment” of sin. On the other hand every sin, even venial, entails an unhealthy attachment to creatures, which must be purified either here on earth, or after death in the state called Purgatory. This purification frees one from what is called the “temporal punishment” of sin. These two punishments must not be conceived of as a kind of vengeance inflicted by God from without, but as following from the very nature of sin. A conversion which proceeds from a fervent charity can attain the complete purification of the sinner in such a way that no punishment would remain.
1473 The forgiveness of sin and restoration of communion with God entail the remission of the eternal punishment of sin, but temporal punishment of sin remains.