Jesus Christ commanded his disciples to preach the gospel to all the world, baptizing all
who believed, in the name of the Father, the Son, and the Holy Ghost. This command was faithfully carried out in the early church. Water baptism is for believers only; those who hear the gospel, believe, and turn to Christ as their Savior. This is the pattern we see throughout the early church, as is seen in the book of Acts. Water baptism is the outward symbolic act, of the regeneration, that has already taken place in the heart ( spirit ). It symbolizes the death of the old life and the birth of the new.

________________________________

MARK 16:15-16   And he said unto them. “Go ye into all the world, and preach the
  gospel to every creature”.
  Vs.16. “ He that believes and is baptized shall be saved; but
  he that believeth not shall be damned”.

MATTHEW 28:19   “Go ye therefore, and teach all nations, baptizing them in the name
  of the Father, and of the Son, and of the Holy Ghost”.

ACTS 8:35-38   Then Philip opened his mouth, and began at the same scripture, and
  preached unto him Jesus.

  Vs.36   And as they went on their way, they came unto a certain water: and the eunuch
  said, “See, here is water, what doth hinder me to be baptized”?

  Vs.37   And Philip said, “If thou believeth with all thine heart, thou mayest”. And he
  answered and said, “I believe that Jesus Christ is the Son of God”.

  Vs.38   And he commanded the chariot to stand still: and they went down into the water,
  both Philip and the eunuch: and he baptized him.

See the following: ACTS 10:1-48

Notice that while Peter was preaching about Jesus they received the Holy Spirit, later they were baptized in water. ( Only born again Christians receive the Holy Spirit ) they became Christians before they were baptized in water. Water Baptism has nothing to do with regeneration.

________________________________