This is the most important “mission” text in the history of the Church:

When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.

It all began, in some ways, at Pentecost. The kingdom preaching of Jesus, the table fellowship boundary-breaking habits of Jesus, and the Jesus Creed-shaping behaviors of Jesus suddenly take on new shape when Pentecost happened.

The empowerment here is for witness but there is a theme to it all: the Spirit transcends human abilities and transforms human abilities. The Spirit takes us to the next level of witness. Mission is about Spirit-empowered witness.

Beverly Gaventa, in her commentary on Acts (The Acts of the Apostles (Abingdon New Testament Commentaries)
) says this: “In some unexplained way, the walls of the house dissolve and the community finds itself outdoors and in the presence of a Jews ‘from every nation under heaven living in Jerusalem'” (74-75).

Spirit-empowered mission means dissolving doors — that is, it means going public with a courage previously unknown.