The apostle is now circling back to 1 Peter 3:18, when he had initially mentioned Jesus’ resurrection (“made alive by the Spirit”) and picking up the broad train of thought he had briefly dropped. Christ suffered for sin to the point of death for the purpose of bringing sinners to God (1 Peter 3:18). That his labours achieved their purpose was proven through his resurrection. Imprisoned demons could destroy so much in Noah’s day but Christ’s resurrection proclaims his victory and so the victory of all those washed of sin as signified in baptism.
21 Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a good conscience, through the resurrection of Jesus Christ,