What does Acts 5:12 mean?
Despite the Sanhedrin's orders not to teach or speak in Jesus' name (Acts 4:18), the apostles continue their ministry right next to the temple. The temple mount is surrounded by covered walkways called porticos. They are popular places for rabbis to teach their students, and anyone else happening by who is interested. It's safe to say none of the other teachers had such a healing ministry. Jesus had said the disciples would do greater works than He (John 14:12), meaning in scale, not power. Now, in order to validate their message, the Holy Spirit has so empowered the apostles that apparently even Peter's shadow can heal (Acts 5:15).Hebrews 2:4 recounts this part of the apostles' ministry. The Holy Spirit attested to the apostles' ministry "by signs and wonders and various miracles." Hebrews 2:1–3 explains why these miracles are important. At the time, they drew people to a saving faith in Jesus. Later, they acted as a reminder of how deserving we are of retribution for our sins and how we should not "drift away" from the message of Jesus' gift of salvation.
Faith should never be dependent on signs, however (John 2:23–25; 4:48). After Thomas finally saw Jesus and affirmed His identity, Jesus said, "Have you believed because you have seen me? Blessed are those who have not seen and yet have believed" (John 20:29). It's unclear why the Holy Spirit allows the church to grow through the healing of the sick and demon possessed. Possibly because before long, persecution would drive the Jesus-followers out of Jerusalem (Acts 8:1–3) and the powerful signs would keep them encouraged as they spread the gospel.