Acts 25:21
But when Paul had appealed to be reserved unto the hearing of Augustus, I commanded him to be kept till I might send him to Cæsar. But when Paul had appealed to be reserved unto the hearing of Augustus, I commanded him to be kept till I might send him to Cæsar.
After Paul appealed to be reserved for the hearing of Augustus, Festus ordered him kept in custody until he could be sent to Caesar in Rome for a hearing before the emperor. The order kept Paul a prisoner while his appeal awaited its hearing and transfer to Caesar. Festus understood the case as turning on questions of Jewish religion and on Jesus' death and resurrection, rather than the accusation he had expected. The wait included delay in securing a suitable ship, which gave Paul time in Caesarea to explain his faith to leading people, including King Agrippa II.
During that detention Paul was brought before Agrippa and a distinguished audience, not for a new trial but to satisfy their curiosity. The prolonged custody while awaiting Caesar's hearing left him exposed to the caprice of officials, since Felix had already held him for years and the emperor's virtually unlimited authority offered no higher restraint. In this setting of chains and facing death under Nero, the verse illustrates faith standing firm against a ruler's power.