I believe that Scripture is talking about the soul or spirit of man being baptized by the Holy Spirit.
There is a baptism for the body and that is what John was doing with water.
There is a baptism for the soul which is by the Holy Ghost.
So there is one baptism to the outward man and one baptism to the inner man.
Ephesians, chapter 4
4": There is one body, and one Spirit, even as ye are called in one hope of your calling;
"5": One Lord, one faith, one baptism,
1 Corinthians, chapter 12
"13": For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit
Acts, chapter 10
"46": For they heard them speak with tongues, and magnify God. Then answered Peter,
"47": Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?
"48": And he commanded them to be baptized in the name of the Lord.