Baptism is the foundational sacrament by which a believer in Christ enters the community of the Church, as by various rites the Jewish child took their place in the community of Israel.
Baptism has two elements identified by Christ in John 3:1-6, water and the Holy Spirit. To the visible action of baptizing with water, already a purification ritual in Judaism, is added an invisible element that only Christ through His merits can give, the spiritual renewal of the individual through the Holy Spirit.
To be baptized, the Church teaches that water must flow on the body of the person (whether by immersion in water or by pouring water across the forehead), while the one baptizing, usually a priest or deacon, says, “I baptize you in the name of the Father and of the Son and of the Holy Spirit” (Mt. 28:19).
Catechism of the Catholic Church 1263. By Baptism all sins are forgiven, original sin and all personal sins, as well as all punishment for sin. In those who have been reborn nothing remains that would impede their entry into the Kingdom of God, neither Adam’s sin, nor personal sin, nor the consequences of sin, the gravest of which is separation from God.
Further, the Catechism says,
Baptism not only purifies from all sins, but also makes the neophyte “a new creature,” an adopted son of God, who has become a “partaker of the divine nature,” member of Christ and coheir with him, and a temple of the Holy Spirit (paragraph 1265).