Baptism does not make you a believer – it shows that you already believe. Baptism does not “save” you, only your faith in Christ and through His power does that occur. Baptism is like a wedding ring – it is the outward symbol of the commitment you make in your heart.
“For it is by grace you have been saved, through faith… it is the gift of God – not by works, so that no one can boast.” – Ephesians 2:8-9