In the 6th chapter of Romans Paul explains it as a symbolic burial with Christ. A washing away of sins by death with Christ. When Paul saw his vision of Christ on the road to Damascus it put him blind and a prophet was sent to him saying "Why tarriest thou, arise and be baptized, washing away thy sins calling on the name of the Lord." Baptism into Christ is one baptism, but it includes both of the water and of the Spirit. Jesus says in the 3rd chapter of John that except a man be born of the water and of the Spirit that he would not be able to enter into the kingdom of heaven. The book of Acts is one of the most important books in the bible because it shows how all these things took place in the early church.