Question 71 Where has Christ promised us, that he will as certainly wash us by his blood and Spirit, as we are washed with the water of baptism?

Answer: In the institution of baptism, which is thus expressed: "Go ye, therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost", Matt.28:19. And "he that believeth, and is baptized, shall be saved; but he that believeth not, shall be damned.", Mark 16:16. This promise is also repeated, where the scripture calls baptism "the washing of regenerations" and the washing away of sins. Tit.3:5, Acts 22:16. (a)

(a) Tit.3:5 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost; Acts 22:16 And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.