The Greek word diadochos means a successor — one who takes the place of another, especially in an official position. It appears in Acts 24:27 where Porcius Festus succeeded Felix as governor of Judea, leaving Paul still imprisoned. The word implies continuity of office even with a change of person.
Paul's imprisonment through two successive Roman governors is a masterpiece of providential irony. Felix kept Paul imprisoned hoping for a bribe; Festus, his successor, inherited both Paul and the problem. Yet through this succession of flawed, self-interested rulers, God was working to bring Paul to Rome (Acts 19:21). The diadochos in Acts illustrates that God's purposes are not contingent on the quality of any particular leader or institution. The succession of corrupt officials actually became the mechanism of Paul's Roman testimony. God's kingdom advances through successors to earthly power who are themselves subject to the King of Kings.