There Were Four!
As the four gospels were written using four authors to four different groups of people, baptism was used as a vehicle to carry the message of salvation using four different messengers to various groups of people. Yet each messenger was focused on one single message: Salvation is only through Jesus Christ; and man's only part is to surrender from his feeble efforts.
John the Baptist
John was sent by the Father to identify his Son Jesus as the Messiah to the nation of Israel and to show their need for a new way to salvation. And he used baptism to do it!
Like the Four Gospels
The four gospels were written to four different groups of people. One of the ways they are described is:
Matthew was to the Jews, Mark to the Romans, Luke to the common people, and John to the Greeks.
Baptism was also given to four different audiences:
John to the Jews basing their relationship with God through the Law; Jesus to all who would listen; the Apostles to Jews leaving the Law and traditions behind; and Paul to the Gentiles.
Jesus
Jesus' message was simple: "I am the way, the truth and the life!" Although he came first to the Jews --and was rejected by most-- He also came to the whole world.
Peter and the Other Apostles
The message that Peter and the other apostles carried to the Jews was for them to have one final washing (baptism) with water to mark the end of their part in trying to keep the Law. It was a way of providing closure to their former way of life.
Paul's Baptism
Paul's message was for the Gentiles and it did not include baptism. The Gentiles didn't need to end their relationship with the Law, they needed to begin a relationship with God.