With a great sum obtained I this freedom - The freedom or privilege of Roman citizenship. From this it would seem that the privilege of being a Roman citizen might be purchased, unless perhaps he refers to the expenses which were necessarily attendant in passing through the proper forms of becoming a Roman citizen. The argument of the tribune in this case is this: “I obtained this privilege at a great price. Whence did you, Paul, thus poor and persecuted, obtain the means of becoming a Roman citizen?” Paul had informed him that he was a native of Tarsus Acts 21:39; and the chief captain supposed that that was not a free city, and that Paul could not have derived the privilege of citizenship from his birth.
But I was free born - I was born a Roman citizen, or I am such in virtue of my birth. Various opinions have been formed on the question in what way or for what reasons Paul was entitled to the privileges of a Roman citizen. Some have supposed that Tarsus was a Roman colony, and that he thus became a Roman citizen. But of this there does not appear to be sufficient proof. Pliny says (Acts 21:27) that it was a free city. Appian says that it was endowed with the privileges of a free city by Augustus Caesar after it had been greatly afflicted and oppressed by wars. Dio Chrysost. says to the people of Tarsus, “He (Augustus) has conferred on you everything which anyone could bestow on his friends and companions, a country (that is, a free country), laws, honor, authority over the river (Cydranus) and the neighboring sea.” Free cities were permitted in the Roman empire to use their own laws, customs, and magistrates, and they were free from being subject to Roman guards. They were required only to acknowledge the supremacy and authority of the Roman people, and to aid them in their wars. Such a city was Tarsus; and, having been born there, Paul was entitled to these privileges of a free man. Many critics have supposed that this privilege of Roman citizenship had been conferred on some of the ancestors of Paul in consequence of some distinguished military service. Such a conferring of the rights of citizenship was not unusual, and possibly might have occurred in this case. But there is no direct historical proof of it; and the former fact that he was born in a free city, will amply account for his affirmation that he was free born. Compare the notes on Acts 16:37.