22:1 “Brothers and fathers, hear the defense that I now make before you.”
2 And when they heard that he was addressing them in the Hebrew language, they became even more quiet. And he said:
3 “I am a Jew, born in Tarsus in Cilicia, but brought up in this city, educated at the feet of Gamaliel  according to the strict manner of the law of our fathers, being zealous for God as all of you are this day. 4 I persecuted this Way to the death, binding and delivering to prison both men and women, 5 as the high priest and the whole council of elders can bear me witness. From them I received letters to the brothers, and I journeyed toward Damascus to take those also who were there and bring them in bonds to Jerusalem to be punished.” (Acts 22:1-5 (ESV)
It’s an amazing thing that Paul has the fortitude to so quickly forgive, and be calm enough to give a defense of himself after almost being torn to shreds just minutes before hand. His defense will not be that he did not just bring Greeks into the temple, but a proclamation of Christ whom this crowd is persecuting. He can identify with that, so he starts there. He doesn’t only let them know that he used to do the same, but he tells his history so that they can understand that he really is one of them. He is a Jew who was brought up in this city, he studied at the feet of Gamaliel.
This would let the people know who he was straight away. In fact to this day we can read Gamaliel and understand how this would have influenced Paul. The history of the Bible doesn’t happen in a vacuum. This is one of the great testimonies of the Christian faith. These places are here. This history happened in the midst of history. People like Gamaliel were real, we have their writings, we know of them from other historians. We actually know a lot about Paul precisely, because we know about Gamaliel.
The crowd at the temple is now willing to listen to Paul, but Paul who once would have brought people to Jerusalem in chains, not will be led out of Jerusalem in those very same bonds.