ISB ~ 1 Peter 3 v21

Baptism … saves you:The clearest statement in the NT that Baptism brings us salvation. It is not only a sign of forgiveness and renewal, but an instrument of grace that actually regenerates (Jn 3:5; Tit 3:5). The Greek word translated as corresponds means “the fulfillment of a type” (Gk. antitypos).

See word study:Type at Rom 5:14.

• The flood is a type of Baptism: the raging waters that cleansed the earth of wickedness (Gen 7:17-24) prefigure the sacramental waters that cleanse the believer of sin (Acts 2:38; 22:16). In both cases, the water that brings judgment on sin is also the water that saves. It is unclear how far Peter intends us to see parallels beyond this basic level of correspondence.

Certainly the story line itself is meaningful in a Christian context:Noah and his family, having built the ark in faith, passed through the waters of judgment (1 Pet 3:20) into a new life and a new covenant with God (Gen 9:8-17). So, too, Baptism is the sacrament of faith (Mk 16:16) that brings us new life (Rom 6:4) and makes us members of the New Covenant (CCC 1219).

not as a removal of dirt:This clarification makes it certain that Peter is referring to the Sacrament of Baptism, an actual washing of the body that could be misunderstood because its effects on the soul are unseen (Heb 10:22). Some scholars read this statement as an allusion to circumcision, which entails the removal of flesh from the body as something unclean (Gen 17:9-14). In this case, Peter would be setting forth a contrast between the physical effect of circumcision and the spiritual effect of Baptism, much as Paul did in Col 2:11-13.