After we believe in Jesus Christ, baptism is an indispensable next step.
The Holy Spirit is present at the time of baptism
With the presence of the Holy Spirit a new life begins.
Baptism is a symbol and image of our past sins being washed away, dying with Christ and rising again with Christ to a new life.
By baptism we declare that Jesus Christ is our Lord and Savior, that He went to the cross to atone* for my sins. (*to pay the penalty for my sins and reconcile me with God) and after three days, He rose again from the dead. From now on Jesus Christ is my King and Lord.