I think we often read past Acts 8:1-4 just to get to Philip’s ministry to Samaria and the Ethiopian eunuch. Nevertheless, these four verses tell us a great deal, and are pretty much continued at Acts 11:19. It seems Luke placed Philip’s ministry to Samaria and the Ethiopian plus Saul’s conversion plus Peter’s going to the Roman centurion and his household right in the middle of this persecution, or to put it another way: between Acts 8:4 and Acts 11:19. It serves as a kind of parenthesis within the persecution and its information helps us to forget what is really taking place. Believers are dying for their faith.
What happened? Well, it seems that the ruling Sadducees finally got what they wanted. They are now able to strike out at the Messianics without fear of causing an uprising among the people (cp. Acts 6:11-12a). Still they are kept from hurting the Apostles, but that won’t last forever as we shall see once we get to the reign of Herod Agrippa in Acts 12. The Pharisees are also in the mix now, and it seems this means Gamaliel (Acts 5:34-40) as well. We couldn’t expect Saul, who grew up under the teaching of this man (Acts 22:3), to revolt against his teacher and side with the Sadducees, whom the Pharisees normally resented and opposed (cp. Acts 23:6). So, we have a united ruling body who lashes out at the Messianic Jews and their decision to do so is supported by the people.
What sort of persecution was this? Was it a minor uproar within Jewish society that could hardly be noticed otherwise? According to Paul (Acts 26:9-11) he entered every synagogue (house in Acts 8:3) and seized believers and brought them before the Sanhedrin for punishment up to and including death. Moreover, during his interrogation of believers, he tried to get them to deny Jesus. He also punished them himself (Acts 26:11) which probably included beatings (cp. Matthew 10:17), and he was an equal opportunity enemy of the faith in that both men and women were included (Acts 8:3; 22:4) in his efforts to stamp out this growing sect (Galatians 1:3). Not only did Saul seek to eradicate the believing community from Jerusalem, but he pursued believers even to foreign cities with the intent of imprisoning them and bringing them to Jerusalem for judgment (Acts 26:11; 9:1-2).
Saul, however, was not on a one-man-mission. On the contrary, he was one among many, but excelled above all (Galatians 1:14). Saul advanced in the Jewish religion by being a good Jew, by doing the bidding of the high priest (Acts 22:5; 26:12), and being a good Jew meant hurling insults at Messianic believers (Acts 8:3) and more. Persecution became state policy, backed up with the approval of the high priest and the Sanhedrin—composed of both Sadducees and Pharisees.
It isn’t said in the text, and neither does Josephus give a reason for the replacement of the officiating high priests during this time, but Caiaphas, Annas’ son-in-law, was removed from office and replaced by Jonathan, Annas’ son. Caiaphas seemed to otherwise have a good rapport with Rome in that he served in that office for about 10 years. Jonathan served less than 2 years before he was replaced by his brother Theophilus. So, in the space of 2years, Jerusalem had three different high priests officiating at the Temple, when prior to this Caiaphas had officiated in that office for about ten years without any interference from Rome. On the face, it seems there is a good argument that Rome really opposed the persecution conducted by the Sanhedrin. Perhaps, leading believers even complained to the Roman governor for how they were being mistreated as was done when James, the Lord’s brother, was killed by another of Annas’ sons (cir. 62 CE). Later in Acts, Luke shows that the believing community enjoyed a relatively good relationship with Rome, in that, believers in Jesus were considered innocuous by Rome, although every other messianic cult was perused and destroyed by the Roman governors ruling Judea and Samaria.
 JOSEPHUS: Antiquities of the Jews; Book 20, chapter 9, paragraph 1.