If a person is water baptized before being saved there has been no redemption. They cannot identify with the death, burial, and resurrection of the Lord Jesus before salvation. So water baptism is only for saved people and it is a picture of what Jesus accomplished in salvation. To repeat, water baptism can never atone for sins. It is just an outward testimony of the inward conversion, the spiritual baptism that occurred at salvation.
Water baptism can never atone for sins.
As covered earlier, only the blood of Jesus can do that. This is a very interesting point. I would assume if water baptism was a part of the salvation process then it would be directly listed as part of the gospel. Below, Paul mentions the gospel and he tells us what that includes. By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.