The book of Acts is written by Luke, who also wrote the book of Luke. It is essentially a continuation of Luke, with the book of Luke covering Jesus’ life and Acts picking up when Jesus returned to heaven. Luke documents an important transition from followers of Jesus mainly being Jews to followers of Jesus coming from many nations and ethnicities. Many see verse 8 as a summary of the entire book.
Like we saw in John 14 and 16, Jesus again promises the Holy Spirit, and an angel promises that Jesus will one day return.