Why were the apostles unafraid of Rome and the Jewish authorities?
They were unafraid because the resurrection had given them unshakable boldness and hope. The living proof of Jesus' resurrection—especially Peter's transformation—convinced them that death was temporary and that Rome or the Jewish authorities could only touch the body of flesh.
Les explains that before the resurrection the apostles were scattered in fear for their lives, and Peter even denied the Lord with an oath. But after the resurrection they had a boldness that no one could shake. Les points to Peter himself as a major proof of resurrection. That same resurrection power meant nothing scared them—Rome did not scare them, the Jews did not scare them. They were so bound in the hope and power of resurrection that they were not afraid of what could be done to the body of flesh, because death is only temporary in light of resurrection power.