John the Baptist was the forerunner of our Lord. As the last and greatest of the Old Testament prophets, he was announcing that the Messiah promised in the Old Testament was soon coming. Until Jesus’ baptism, he did not know for certain that, indeed, Jesus was this Messiah. John’s baptism was a baptism of repentance, an acknowledgement of sin, and of the need for the forgiveness of sins which Messiah (the “Lamb of God”) would bring about. The baptism was the symbol of their acknowledgement of sin, and of their need for a Savior. It was a preparatory baptism, but (as we see in Acts 19) it did not preclude the need for “believer’s baptism,” once they had come to faith in Jesus as that promised Messiah. This is why the church baptized new believers, and why believers today should be baptized as well.