[The Church] has received the keys of the Kingdom of heaven so that, in her, sins may be forgiven through Christ's blood and the Holy Spirit's action. In this Church, the soul dead through sin comes back to life in order to live with Christ, whose grace has saved us. 526
Catechism number 985
Baptism is the first and chief sacrament of the forgiveness of sins: it unites us to Christ, who died and rose, and gives us the Holy Spirit.