Robert C. Tannehill’s 2-volume work, The Narrative Unity of Luke-Acts, is full of sharp insights. At least that’s true of the bit I’ve read. He points out, for example, the basic structural device of using prophetic quotations and long speeches to introduce each of the major figures in his history:

Luke 3: John the Baptist is introduced with a lengthy excerpt from his preaching and a quotation from Isaiah 40.
Luke 4: Jesus is introduced with a sermon at Nazareth, which describes the fulfillment of Isaiah 61.
Acts 2: The Petrine phase of Acts is introduced by Peter’s Pentecost sermon, with the important quotation from Joel 2.
Acts 13: The Pauline phase of Acts is introduced by a sermon from Paul that concludes with a sharp rebuke quoted from Habakkuk.

One of the things that Tannehill draws out from this is that “phrases used to describe the mission of John the Baptist are reused in describing the work of Jesus’ followers” (p. 49). John goes as a messenger before Jesus (Luke 7:27), and when Jesus approaches Jerusalem He sends messengers ahead of Him (9:52; aggelos is the Greek in both passages). Even in Acts, Peter instructs the people in the same way John had done: When they ask “What shall we do” (Acts 2:37; cf. Luke 3:10, 12, 14), Peter tells them to repent and be baptized for the remission of sins. At the end of Acts, Paul is saying virtually the same thing (Acts 26:20 with Luke 3:8). As Tannehill summarizes, “Jesus’ witnesses, like John, are prophetic preachers of repentance. What John began, they continue, for John’s call to repentance remains important. The narrator’s portrait of John has a continuing significance for the narrative, for in significant ways John is a ‘prototype of the Christian evangelist’” (p. 49).

Though Tannehill does not draw this conclusion, this implies that the whole apostolic mission is a mission of “preparation,” just as John’s was. John prepared for the coming of the Lord in the flesh, and the apostles also “went before” Jesus to prepare the apostolic generation for the coming of the Lord in judgment, which took place in A.D. 70.