What does Acts 28:20 mean?

Paul is in a predicament. He is finally in Rome, but he is under house arrest. He wants to explain to the Jews in Rome that Jesus of Nazareth is the Jewish Messiah. However, at the moment, his ministry is surrounded by malicious rumor. To reach the Jews, he must first explain why he is in such a state.

In short, the Sanhedrin accused him of crimes against the Mosaic and Roman laws—capital offenses (Acts 24:5–6; 25:7). He is innocent, but the Roman governors were fearful of the Jewish leaders and refused to give him justice by releasing him (Acts 24:22–27; 26:31). In fact, he could have brought up charges of false accusation against the Sanhedrin, and they could have been executed. Paul refrained, however (Acts 28:17–19).

Paul has been charged with teaching that Jews shouldn't obey the Mosaic law, bringing a Gentile into the temple (Acts 21:20–21, 27–29), starting riots, leading an illegal religious sect, and profaning the temple (Acts 24:5–6). But through it all, he has insisted that the core of his "crime" is his belief that the Messiah has come. He believes—and he has proven numerous times—that Jesus of Nazareth rose from the dead and fulfills the prophecies of the Messiah found in the Jewish Scriptures. He is happy to be in chains if that's what it takes to share that message (Ephesians 6:20). In fact, he finds both safety and freedom of speech while chained to a Roman guard (Acts 28:30–31).