Acts 21-26 are often called the trial speeches. The trial speeches function to drive the plot toward its end, by supplying the pragmatic reasons for Paul’s journey from Jerusalem to Rome, yet what can be overlooked it that this is divinely appointed:
11 The following night the Lord stood near Paul and said, “Take courage! As you have testified about me in Jerusalem, so you must also testify in Rome.” Acts 23:11
The early stages see violent opposition from the Jews. Yet through a chain of events Paul begins his journey to Rome.
In the end the trial speeches are an description of the purposes of God in the gospel of salvation, the hope of resurrection for the world through Jesus’ resurrection (26:6, 16-18, 22-23).