Rather those folks who are Bible only based Christians simply forgot one thing, towards the end of Mathew’s Gospel, in what became known as “the great commision”.
http://www.biblegateway.com/passage/?search=Matthew%2028:16-20
“Matthew 28:16-20
New Revised Standard Version Catholic Edition (NRSVCE)
The Commissioning of the Disciples
16 Now the eleven disciples went to Galilee, to the mountain to which Jesus had directed them. 17 When they saw him, they worshiped him; but some doubted. 18 And Jesus came and said to them, “All authority in heaven and on earth has been given to me. 19 Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 and teaching them to obey everything that I have commanded you. And remember, I am with you always, to the end of the age.”[a]
and why would they be in need of baptism
because they had placed their trust in Christ...hence the need for baptism.