Luke was a theologian. He wrote the Gospel of Luke first and then the Book of Acts. Luke traveled with and was a close associate of Paul. Luke understood both the sanctifying work of the Holy Spirit and that which Paul taught in his letters as well as the empowering work of the Holy Spirit as it related to the prophetic gifts and ministry.
Luke could have included many things in the book of Acts that he did not include. He specifically included the accounts about the Holy Spirit empowering the early church because he had an authorial intent in emphasizing certain theological truths. It becomes obvious to even a beginning bible student when reading through the book of Acts that there seems to be attention drawn to this normative experience of being filled with the Holy Spirit and speaking in tongues. An exuberant, praising of God or magnifying God with an emotional demonstration that usually specifically says it included tongues and when this is not specifically mentioned, there is prophesying, magnifying God, etc.
I recently heard someone say that it is only mentioned 5 or 6 times as if that was not enough to make is such a big deal, which made me chuckle because the fact that it is mentioned 5 or 6 times in 28 chapters proves conclusively that it was A BIG DEAL to Luke.
I think that the reading of the book of Acts proves that there is a regeneration work of the Holy Spirit and then an additional empowering for ministry work of the Holy Spirit.
Remember Jesus breathed on them and said receive the Holy Spirit after his resurrection but before the day of Pentecost. That was the regeneration work. The day of Pentecost was the empowering work.
Remember also that Jesus said to go into all the world and preach the Gospel to all nations baptizing them in the name of the Father, Son, and Holy Ghost, but then he said.. wait in the city of Jerusalem until you be endued with power from on and then you will be witnesses for me in Jerusalem, Samaria, Judea and the uttermost parts of the earth.
Today we are still being sent with the same great commission. You are saved, born again and have the Holy Spirit enter into you by faith to regenerate you and start you on this sanctification journey. And you are given the commission to go ye therefore into all the world and preach the Gospel to every creature, .. but then he also still says.. be endued with power from on high in order to fulfill that commission with the empowerment of the Holy Spirit and this is a subsequent experience to regeneration.
Now I know that not everyone agrees with this, but this is my understanding of what Luke was faithful to present from the book of Acts.
If you want to know more or if you are interested in examining some of the best hermeneutics from highly respected top theologians published to date on this subject look up Lucan Pneumatology and authurs such as Roger Stronstad, Robert and William Menzies, Gordon Fee, as starters and you will find plenty of others from their bibliographies.