we: The shift from they to we suggests that Luke traveled with Paul from Troas to Philippi (16:10–17). Later, Luke joined Paul again at Philippi and sailed with him to Troas. Then they went to Miletus, and from Miletus to Jerusalem (20:5–15; 21:1–18).
After Paul spent two years in prison in Caesarea, Luke traveled with him to Rome (27:1–28:16).