Baptism is going public about your faith in Jesus and communicating to the world your heart-felt commitment to following Him. It's the next step after salvation.
Baptism is an outward expression of an inward change. It's a public declaration of how Jesus changed your life. Being baptized shows others that you've decided to follow Jesus, and allows them to celebrate this decision with you (Acts 16:31-34).
Why does baptism matter? Jesus instructs us to be baptized and set the example by being baptized (Matthew 28:19-20, Mark 1:9).
Obedience to Jesus shows we believe and follow Him. (1 John 2:3). Because Jesus went public about His love for us, we can go public about our love for Him. Being baptized shows that we turn away from a life of sin toward Jesus, the only one who can change us (Acts 2:38-41).