Heidelberg Catechism - Lord's Day 26

69. Q . How does holy baptism remind and assure you that Christ’s one sacrifice on the cross benefits you personally?
      A. In this way: Christ instituted this outward washing and with it promised that, as surely as water washes away the dirt from the body, so certainly his blood and his Spirit wash away my soul’s impurity, that is, all my sins.

70. Q . What does it mean to be washed with Christ’s blood and Spirit?
      A. To be washed with Christ’s blood means that God, by grace, has forgiven our sins because of Christ’s blood poured out for us in his sacrifice on the cross.

To be washed with Christ’s Spirit means that the Holy Spirit has renewed and sanctified us to be members of Christ, so that more and more we become dead to sin and live holy and blameless lives.

71. Q . Where does Christ promise that we are washed with his blood and Spirit as surely as we are washed with the water of baptism?
      A. In the institution of baptism, where he says:

“Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit.”

“The one who believes and is baptized will be saved; but the one who does not believe will be condemned.”

This promise is repeated when Scripture calls baptism “the water of rebirth” and the washing away of sins.