Baptism doesn’t make you a Christian. Faith in Jesus is what makes you a Christian. However, Baptism is a sacrament of the church that is very important for several reasons.
First of all, it is an act of obedience. Being a follower of Christ means living life in obedience to Him. Jesus himself said that disciples (or followers of Christ) should be baptized (Matthew 28:19-20).
Secondly, Baptism is a public declaration of faith in Christ that illustrates the death, burial, and resurrection of our Savior (Romans 6:4). It is an outward sign of an inward commitment to Jesus.