Acts 22:28 – The tribune answered, “I bought this citizenship for a large sum.” Paul said, “But I am a citizen by birth.”
So how is Paul, who is a Jew (Acts 21:39; Gal 2:15) a free born Roman citizen? Although we may never know for sure, one theory that stands out has to do with his family. For Paul to be born free, his father or grandfather (maybe even farther back) must have been set free either by purchase or by decree from a Roman official. When this happens the family will typically take on the name of the one who set them free as a testimony and assurance with which you could validate the claim. We see a sample of this in Acts 23:26, where the commander we know as Lysias (24:7) also bears the name of Emperor Claudius, the one of whom Lysias purchased his freedom (22:28). Now we never get to hear of a first name for Paul, but there was likely one that his family bore because of being set free.
Just how his family was set free is another matter. It is believed that it must have something to do with the family business, which was tentmakers. You have a Roman army that travels a lot, and so for lodging they will need temporary quarters, thus they needed many tents. So it is plausible that in the manufacturing of Roman tents that Paul’s father or grandfather was awarded citizenship. Or it is possible that this business of tent making for Rome was profitable enough to buy their citizenship.