When they had entered the city, they went up to the (a)upper room where they were (b)staying; that is, (c)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.
This might be the same upper room that the disciples and Jesus had their Last Supper, Lk 22:7-13; it is interesting to think that maybe Jesus rented this room not just for the night, but for the next couple of months in anticipation of the events that would follow.
v.13 (c) this is the same list of apostles as in Lk 6:14-16 with the exception of course of Judas Iscariot. There is however a change in the order and placement of the names. In the Bible, it is very common that the order of a name in a list, like a genealogy, is not necessarily the order from oldest to youngest, but instead the order is made by importance.
We see that here, as compared to the list in Lk 6-14-16. In the list in Acts, Peter and John have been elevated to a high standing as leaders among the apostles, thus they are listed first instead of with their brothers as we see in the list from Luke.
The amount of persecution they were experiencing is more than can be imagined. The Pharisees wanted to kill them and Romans wanted to arrest them for causing a disturbance.
They had just spent forty days on and off with Jesus after the resurrection, but they did not yet have the power of the Holy Spirit to give them confidence and boldness. My guess is they were following the Lord’s command to stay in Jerusalem, but still being very discreet and quiet; probably still behind locked doors.
Jesus had spent the last 40 days opening their eyes to the scriptures; showing them that His suffering that had just taken place was, in fact written hundreds of years before as prophecy. He was building their faith and confidence in the word; giving them insight and understanding to His plan.