After the resurrection, Jesus walked and talked with the disciples for 40 days then ascended into heaven to be seated at the right hand of his Father. The disciples must have felt dismay and loss all over again. When they gathered together, on the day now known as Pentecost, they probably weren’t feeling confident and upbeat. There was a strong wind and the Holy Spirit came on them, they saw flames that seemed to rest on each one, without burning them. After that, the disciples were filled with supernatural courage and began to speak in different languages, witnessing to the death and resurrection of Jesus. From that point, the church and the spread of the gospel was unstoppable. Signs and wonders followed where the disciples went.
The difference for the first century Christians was the Holy Spirit coming to live in them. They were “clothed with power from on high” just as Jesus promised in Luke 24:49. The Holy Spirit gives wisdom, discernment, courage and strength to those he indwells. That same indwelling is available for Christians today.