Baptism is an outward expression of what has happened inwardly in a believer’s life. It is a picture of the believer identifying with Christ’s death, burial, and resurrection.
"Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life." Romans 6:3-4
We do not believe that salvation is earned through baptism, rather, salvation is recieved by grace through faith in Jesus Christ, not by works of any kind, including baptism (Ephesians 2:8-9). In light of accepting Jesus as Lord and Savior, baptism is the the public display of the believer identifying with the gospel of Christ. The action of being immersed in the water symbolizes dying and being buried with Jesus. While the action of coming out of the water is an illustration of being resurrected with Jesus.
Baptism is important because it is a step of obedience, a public proclamation of faith in Christ and commitment to Him, and identification with Jesus' death, burial, and resurrection.