"'Now it happened, when I returned to Jerusalem and was praying in the temple, that I was in a trance and saw Him saying to me, "Make haste and get out of Jerusalem quickly, for they will not receive your testimony concerning Me." So I said, "Lord, they know that in every synagogue I imprisoned and beat those who believe on You. And when the blood of Your martyr Stephen was shed, I also was standing by consenting to his death, and guarding the clothes of those who were killing him." Then He said to me, "Depart, for I will send you far from here to the Gentiles"'" (Acts 22:17-21).
God had great plans for Paul as an evangelist primarily to the Gentiles. His past as a strong persecutor of Christianity would be a continual challenge for him in a couple ways. After obeying the gospel, Paul preached to many Jews and loved them dearly, but most would not accept the good news of Jesus. Because Paul was a Pharisee turned Christian, this would presumably give him insights into how to best reach out to Jews with the gospel. That's what Paul thought at least, but God knew the hearts of the Jews would not be turned so easily. I can only imagine how much the religious elite hated Paul for his religious change and how much this motivated them to make life difficult for him. Thus, God sent Paul far from Jerusalem for long periods of time to teach among the non-Jews.
"And they [the mob that was still gathered] listened to him until this word [i.e., "Gentiles"], and then they raised their voices and said, 'Away with such a fellow from the earth, for he is not fit to live!' Then, as they tore off their clothes and threw dust into the air, the commander ordered him to be brought into the barracks, and said that he should be examined under scourging, so that he might know why they shouted so against him" (Acts 22:22-24).
It appears Paul held the attention of his audience until he uttered the word "Gentiles." This sent the prejudiced mob from a state of silent smoldering into a fit of explosive rage! They would not accept the notion that God would commission someone to extend His grace to the Gentiles (whom they viewed as dogs)! They called for Paul's life as they tore off their outer garments and threw dust into the air. The commander, who no doubt allowed Paul to speak in hopes of making sense of this situation, is likely disappointed and agitated now. Paul spoke in Hebrew, which Lysias presumably would have been unable to follow. Furthermore, even if he could understand Paul's words, he would not have been able to consequently ascertain the real reason behind the mob's rage since Paul did not attempt to defend himself in a traditional way (e.g., "I did not take any Gentiles into the temple"). So, the commander feels like he has no other choice than to proceed with his initial plan; that is, to examine Paul privately in the barracks. This intended examination would include a scourging (a brutal form of whipping that, if survived, left a person's back in a bloody, torn condition).
"And as they bound him with thongs, Paul said to the centurion who stood by, 'Is it lawful for you to scourge a man who is a Roman, and uncondemned?' When the centurion heard that, he went and told the commander, saying, 'Take care what you do, for this man is a Roman.' Then the commander came and said to him, 'Tell me, are you a Roman?' He said, 'Yes.' The commander answered, 'With a large sum I obtained this citizenship.' And Paul said, 'But I was born a citizen.' Then immediately those who were about to examine him withdrew from him; and the commander was also afraid after he found out that he was a Roman, and because he had bound him" (Acts 22:25-29).
As preparation is being made to examine Paul under scourging, Paul speaks up to a nearby centurion, inquiring about the legality of scourging an uncondemned Roman citizen. Clearly, Paul is implying that he is such, and the soldier believes him, reporting this information to the commander. Lysias then speaks to Paul, verifying this information. It was a capital offense to lie about Roman citizenship, but Paul was not lying. He revealed this truth about himself at an opportune time in order to spare himself some intense pain (there is nothing wrong with using civil laws to our advantage, as long as we are faithful to God in so doing). The commander acknowledges the tremendous blessing that Roman citizenship is (for he paid dearly to acquire such citizenship for himself). Yet, Paul was born with this citizenship and it spared him from being scourged on this occasion. Paul's Roman citizenship made Lysias very nervous, since they had already bound the apostle to the whipping post with thongs before Paul spoke up. That very act could not be rightly done to an uncondemned Roman. Would Paul cause problems for Lysias now as a result? Lysias is certainly concerned about that possibility.