Peter made clear that he did not want readers to think he was referring to water baptism when he specifically said “not the removal of dirt from the flesh” (1 Peter 3:21). That he was actually referring to a spiritual reality when he wrote “baptism now saves” is also clear from the phrase, “an appeal to God for a good conscience—through the resurrection of Jesus Christ” (v. 21). The only baptism that saves people is dry—the spiritual one into the death as well as the resurrection of Christ—of those who appeal to God to place them into the spiritual ark of salvation safety (cf. Romans 10:9-10).
Just as the Flood immersed all people in the judgment of God, yet some passed through safely, so also his final judgment will involve everyone, but those who are in Christ will pass through securely. The experience of Noah’s family in the Flood is also analogous to the experience of everyone who receives salvation. Just as they died to their previous world when they entered the ark and subsequently experienced a resurrection of sorts when they exited the ark to a new post-Flood world, so all Christians die to their old world when they enter the body of Christ (Romans 7:4-6; Galatians 2:19-20; Ephesians 4:20-24). They subsequently enjoy newness of life that culminates one day with the resurrection to eternal life. . . .
Therefore, God provides salvation because a sinner, by faith, is immersed into Christ’s death and resurrection and becomes His own through that spiritual union. Salvation does not occur by means of any rite, including water baptism.
John MacArthur, The MacArthur New Testament Commentary: 1 Peter, p. 217-218