Let me make an observation here about the "empowering" of the church at Pentecost. More accurately, it is the re-empowering.
Throughout Jesus earthly ministry, his disciples were empowered by the Christ himself. Remember when he sent out the seventy (Luke 10)? When they returned, they reported to Jesus "even the demons were subject to us."
Remember when the disciples handed out five loaves and two fishes to 5,000 people. They operated in the power of the Lord Jesus.
I find it interesting that they operated that way all the way up to the Crucifixion. Then, after the resurrection, Jesus ascended and left them. It appears that he left them without his power. He told them, however that they would receive power from the Holy Spirit, and it would come in a few days. This power would drive their witnessing.
So, for the next few days, the disciples, mother Mary, and the other women, his brothers and other followers gathered in that upper room for prayer and supplication. I have read more than one writer who thinks they were hiding there.
We know the rest of the story. The Holy Spirit did something that He had never done before. He empowered every believer. Those early disciples, whom Jesus had empowered, were left powerless when He ascended, but re-empowered.