Baptism
The Sacrament of Baptism, the first of the three sacraments of initiation, is also the first of the seven sacraments in the Roman Catholic Church. It removes the guilt and effects of Original Sin and incorporates and welcomes the baptized into the Church, the Mystical Body of Christ on earth.
"I baptize you in the name of the Father, and of the Son, and of the Holy Spirit."
(the "Trinitarian Formula," from Matt 28:19)