1 Peter 4:12

12 Beloved, do not be surprised at the fiery ordeal among you, which comes upon you for your testing, as though some strange thing were happening to you;

The fiery ordeal could be the burning of Rome (which Christians were blamed for), or generally, all the Christian persecution (which was happening at that time). Peter wanted them to know that God allows it, and even designs it, for their testing and to strengthen their character.