In the Acts of the Apostles, there is a short interval of days between the Ascension of Jesus and the coming of the Holy Spirit at Pentecost.
What happened during those days? What did the apostles do between the Ascension and Pentecost?
Devoted themselves to prayer
Immediately following Jesus’ ascension, the apostles and the Virgin Mary gathered together in the upper room to pray. This is the same location where Jesus celebrated the Last Supper.
All these devoted themselves with one accord to prayer.Acts 1:14
Replaced Judas with Matthias
Besides prayer, they were also quite active during these days. The Acts of the Apostles explains,
“During those days … they gave lots to them, and the lot fell upon Matthias, and he was counted with the eleven apostles” (Acts 1:15, 26).
Gathered for the Jewish feast of Pentecost
The apostles and the Virgin Mary made the necessary preparations for the Jewish feast of Pentecost.
Pentecost is the Greek name for the festival known as the Feast of Weeks, or Shavuot in Hebrew.
It is, together with Pesach and Sukkot, one the three pilgrimage feasts of Israel, during which each adult male was required to be present in Jerusalem (cf. Ex 23:14-17).
This helps explain why all were present in Jerusalem, and also gives some insight into what they may have been doing during this time.