What is a sacrament?

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.–CCC 1131

The Holy Spirit prepares the faithful for the sacraments by the Word of God and the faith which welcomes that word in well-disposed hearts. Thus the sacraments strengthen faith and express it.—CCC 1133

The fruit of sacramental life is both personal and ecclesial. For every one of the faithful on the one hand, this fruit is life for God in Christ Jesus; for the Church, on the other, it is an increase in charity and in her mission of witness.—CCC1134