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.