7. What is baptism?

Romans 6:1-6 What shall we say, then? Shall we go on sinning so that grace may increase? 2 By no means! We died to sin; how can we live in it any longer? 3 Or don't you know that all of us who were baptized into Christ Jesus were baptized into his death? 4 We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life. 

    RO 6:5 If we have been united with him like this in his death, we will certainly also be united with him in his resurrection. 6 For we know that our old self was crucified with him so that the body of sin might be done away with, that we should no longer be slaves to sin

Acts 8:36-38 As they traveled along the road, they came to some water and the eunuch said, "Look, here is water. Why shouldn't I be baptized? 37 Philip said, "If you believe with all your heart, you may." The eunuch answered, "I believe that Jesus Christ is the Son of God." 38 And he gave orders to stop the chariot. Then both Philip and the eunuch went down into the water and Philip baptized him.

We go down into the water.  It is there that we experience a death, burial, and resurrection.  We die to our sins and our old life.   That life is buried beneath the waters of baptism just as Jesus was buried in the tomb.  We rise from the waters of baptism and experience our resurrection from the dead old way of life we lived previous to following Jesus to live for and serve the Lord.