Albert Barnes Commentary Acts 1:13

"And when they were come in, they went up into the upper chamber, where they were abiding; both Peter and John and James and Andrew, Philip and Thomas, Bartholomew and Matthew, James [the son] of Alphaeus, and Simon the Zealot, and Judas [the son] of James." — Acts 1:13 (ASV)

Were come in. To Jerusalem.

They went up into an upper room. The word—uperwon—here translated upper room, occurs only four times in the New Testament: Acts 9:37, She (Dorcas) was sick, and died: whom when they had washed, they laid her in an upper chamber, Acts 9:39; and Acts 20:8, And there were many lights in the upper chamber, where they were gathered together.

The room so designated was an upper chamber used for devotion, for placing the dead before burial, or occasionally for conversation and other similar purposes. Here, it evidently means the place where they were assembled for devotion.

Luke 24:53 says they were continually in the temple praising and blessing God. Some have supposed that the upper room mentioned here was one of the rooms in the temple. However, there is no evidence for this, and it is not very probable.

Such a room was a part of every house, especially in Jerusalem. They probably selected one where they could be together, and yet be secluded enough that they might be safe from the Jews.

Where abode. That is, where they were staying. This does not mean that this was their permanent dwelling place, but they remained there waiting for the descent of the Holy Spirit.

Peter, etc. All the apostles whom Jesus had originally chosen were there, except Judas (Luke 6:13–16).