I’d suggest reading the Catechism:
An indelible spiritual mark . . .
1272 Incorporated into Christ by Baptism, the person baptized is configured to Christ. Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation.83 Given once for all, Baptism cannot be repeated.
1273 Incorporated into the Church by Baptism, the faithful have received the sacramental character that consecrates them for Christian religious worship. The baptismal seal enables and commits Christians to serve God by a vital participation in the holy liturgy of the Church and to exercise their baptismal priesthood by the witness of holy lives and practical charity.
1274 The Holy Spirit has marked us with the seal of the Lord (“Dominicus character”) “for the day of redemption.” “Baptism indeed is the seal of eternal life.” The faithful Christian who has “kept the seal” until the end, remaining faithful to the demands of his Baptism, will be able to depart this life “marked with the sign of faith,” with his baptismal faith, in expectation of the blessed vision of God - the consummation of faith - and in the hope of resurrection.
1279 The fruit of Baptism, or baptismal grace, is a rich reality that includes forgiveness of original sin and all personal sins, birth into the new life by which man becomes an adoptive son of the Father, a member of Christ and a temple of the Holy Spirit. By this very fact the person baptized is incorporated into the Church, the Body of Christ, and made a sharer in the priesthood of Christ.
