It’s an outward expression of an inward change and that change is a personal decision to accept Jesus as your personal Lord and Savior.
When you are baptized, you are in fact visually preaching the gospel. As you stand in the water waiting to be baptized, you symbolize Jesus dying on the cross. As you are lowered into the water, you symbolize Jesus buried in the tomb. As you are raised from the water, you symbolize Jesus rising from the dead. Just like Jesus, this is a picture of us dying to sin and being covered with God’s forgiveness and being raised to follow Jesus for life. Romans 6:4
Baptism is also a symbol; like a wedding ring symbolizes that I am married and committed to my spouse. Just as the ring doesn’t make me married, being baptized doesn’t save me but shows others that I have made a commitment to Jesus.