Baptism is the physical act of being submerged in water. It expresses a spiritual truth, and it declares that we are, symbolically, sharing with Christ in His death and resurrection. Obviously, we do not truly die because of our sin, as Jesus did, but it is a public testimony of the fact that Christ’s sacrifice is valid. In the same was that Jesus died for mankind, we die symbolically to the old lifestyle. When we enter the water and are totally submerged, it symbolizes the burial of the old sinful nature. The nature stays “buried” under water and the person is symbolically raised from the dead into a new life with Christ. This is, in essence, the public declaration that we will live for Him as His disciples.
Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life.” Romans 6:4.