Chapter 20 ends with a warm farewell by Paul to his closest friends and companions. Chapter 21 opens with the journey back to Judea. Paul wants to get back to Jerusalem. We find warnings that it's not going to go well there . . .
Paul is determined, his companions hang with him, the pace quickens as the narrative becomes more detailed and Paul's life moves into a decidedly different phase . . .
Commentary excerpts, including background information about the Nazarite vow, are found here.