What does Acts 5:15 mean?
The people of Jerusalem are flocking to Solomon's Portico, next to the temple, to see the lead Jesus-followers. They are notable for more than just the healings they perform. Two of them were arrested by the Sanhedrin, the Jewish ruling court, who ordered them to stop preaching in Jesus' name (Acts 4:18). And yet here they stand, boldly using Jesus' name to heal and telling the crowd about His resurrection. In addition, the men seem to have the ability to discern the intents of the people around them and even predict their deaths (Acts 5:1–11). God is obviously empowering these men.Jesus promised the Twelve that after they received the Holy Spirit, they would be able to do greater works than He (John 14:12). Obviously, Jesus' works included dying on the cross for our sins and rising again for our redemption, and there is no greater work than that. But it's reasonable to conclude that over the course of their ministries, the disciples performed more healing miracles than Jesus in His three years.
The text doesn't say if Peter's shadow actually heals, only that this was something many in the public believed. It's not entirely impossible that it would. A very sick woman believed that just touching the hem of Jesus' robe would heal her—and she was right (Mark 5:25–29). In Ephesus, the Holy Spirit so blessed Paul's ministry that cloth that had touched Paul healed people (Acts 19:11–12). Throughout His ministry, however, Jesus was careful to say that it isn't the touch or the cloth that heals but faith (Mark 5:34). Such is the same case here, whether Peter's shadow was actually associated with healing or not. The text doesn't say if everyone who touches Peter's shadow understands the work of Jesus, but they certainly believe that the power of God is on Peter.