Albert Barnes on Acts 25:21

But when Paul had appealed. Acts 25:11.

To be reserved. To be kept; not to be tried at Jerusalem, but to be sent to Rome for trial.

Unto the hearing. Margin, "the judgment." That Augustus might hear and decide the cause.

Of Augustus. The reigning emperor a this time was Nero. The name Augustus--σεβαστου--properly denotes that which is venerable, or worthy of honour and reverence. It was first applied to Caesar Octavianus, who was the Roman emperor in the time when our Saviour was born, and who is usually called Augustus Caesar. But the title continued to be used of his successors in office, as denoting the veneration or reverence which was due to the rank of emperor.

(2) "the hearing of Augustus" "judgment"