About that time Herod the king laid violent hands upon some who belonged to the church. He killed James the brother of John with the sword; and when he saw that it pleased the Jews, he proceeded to arrest Peter also. This was during the days of Unleavened Bread.
Acts 12:1–3 (RSV)
Herod calculated that persecution of the Christians would work in his favor. The leaders of the Temple mistrusted them. The Romans did not like anyone who might upset the balance of power in the Empire.
It became apparent that persecuting the Church was well received; he took the next step, upping the violence, and killed James. As he heard more voices approving of his actions, he arrested St. Peter, most likely with the intent of some spectacular death to please the crowds.
Evil seeks more evil as its lust for control over all things grows and grows. The more wickedness it does, the more it seeks more perverse sins ever. Jesus teaches us that we are never to return evil for evil, for it will overwhelm us.
This passage serves as a reminder and a warning to the Church. We are reminded that the world can turn against us at any moment. If the world sees that it is to its advantage to persecute the Church, it will do so, convinced it is doing good.
Our Lord has promised that the Church will endure; not even the gates of hell will prevail against it.