The baptism of John was focused on preparing people for the coming of God whereas the baptism of the Holy Spirit has to do with empowering the apostles for their witnessing task.1 The coming of the Holy Spirit would also serve as proof that the Messiah has come, as stated by John (Luke 3:15–18).
5 for John baptized with water, but you will be baptized withthe Holy Spirit not many days from now.”