When Paul was arrested by the Romans at the end of 21, he could have played the Roman citizen card then but it seems that he delayed in order to bear witness to what God had done on the road to Damascus.
After sharing, he then makes use of his Roman citizenship, it would seem, that he might continue to share. But if he had played that card earlier he would not have had the opportunity to tell the people his story.
His story? If you remember that darkness fell on Jesus at noon, Paul describes seeing light at noon! First, how do you see light brighter than the noontime sun? Second, he sees the light at noon because Jesus took the darkness at noon.
Dying to self will often look something like what Paul does here. He had particular rights that he decided not to make use of so that he could tell the story of the One who died and was raised!
You might point out that Paul didn’t share with them his understanding of the cross and resurrection. You are right, but I’m certain that he would have. The scene is playing out much like Jesus’s last hours. So, I guess you could say he is sharing Jesus (putting him on display) in his own sufferings.