Acts of the Apostles
From its beginning, it's apparent that the Book of Acts is a continuation of the Gospel of Luke. The writing style in Acts will strike any reader of Luke's Gospel as familiar. He opens with a one-sentence thesis statement:
The “former treatise” is the Gospel that Luke also addressed to Theophilus, whether that is an actual person or a collective name for all the lovers of God (as mentioned previously, the literal translation of Theophilus) likely to read his books. Note the King James Version's use of “passion” as Luke's word for the suffering and death of Jesus, if any wonder about the origin of that term. Also note that the forty days' sojourn of Jesus with his disciples after the resurrection compares with the forty days he was tested by Satan in the wilderness before beginning his ministry. What the disciples were to wait for in Jerusalem was the coming of the Holy Spirit and the official birthing of the Church of Christ at Pentecost.
Unlike Matthew and Mark, Luke didn't include the Great Commission in his Gospel, but recaps it at the beginning of Acts as a transition to Pentecost. “You shall receive power when the Holy Spirit comes upon you. And you will witness to me in Jerusalem and in all Judea, Samaria, and to the end of the earth” (see Acts 1:8). Luke also elaborates a bit on the Ascension: “And when he had spoken these things, while they watched, he was taken up. And a cloud received him out of their sight. And while they stood gazing toward heaven as he went up, two men in white apparel stood by them and said, ‘Men of Galilee, why do you stand gazing up into heaven? This same Jesus who has been taken up from you into heaven shall come in like manner as you have seen him go into heaven’” (Acts 1:9).