The way it concludes Luke’s Gospel is how it begins in Acts. Acts is really Luke: Part 2. Here we get the story of these individuals that were commanded to stay in Jerusalem, because Jesus had previously said He must depart so that the Holy Spirit can come.
So, the book of Acts is the manifestation of the Spirit which is the continuation of the work of Jesus Christ on planet Earth. When Jesus ascends, and the angels show up and say, “This same Jesus, who has been taken from you into heaven, will come back in the same way you have seen him go into heaven.” He’s coming back to planet Earth, but in the meantime, there’s a responsibility for those that have identified with Christ through the power of the Spirit. The charge to those individuals was to be witnesses in Jerusalem and Judea and Samaria and the very ends of the earth. This new era is for the Jews and Gentiles, as Paul would say “first to the Jew, then to the Gentile.”