Dear Theophilus, in the first volume of this book I wrote about all that Jesus began to do and teach until the day he said goodbye to the apostles, those he had chosen through the Holy Spirit, and was taken to heaven. After his death, he presented himself alive to them, in different places, for a period of forty days. In these face-to-face meetings, he guided them on matters concerning the Kingdom of God. Between meetings and meals, he advised them not to leave Jerusalem, but to "wait for what the Father has promised: the promise you have heard from me. John baptized with water, but you will be baptized with the Holy Spirit. And that will happen soon".

The last time they got together, they asked, "Teacher, will you restore the Kingdom to Israel now? Is the time right?" He replied, "You must not try to find the time. It is the Father's responsibility to determine the time. You will receive the Holy Spirit, and when he comes you will be my witnesses in Jerusalem, throughout Judea and Samaria, and even in us ends of the earth". Those were his last words.

As they watched, he was taken away and disappeared in a cloud. They stood there, looking up at the empty sky. Suddenly, two men dressed in white appeared and said, "Galileos! Why are you standing still, looking up to heaven? This same Jesus you saw taken to heaven will return, just as surely and mysteriously as He left." 

Going Back to Jerusalem 

They left the Mount of Olives and returned to Jerusalem, about a kilometer away. They went to the room they used as a meeting place, which was on the top floor of a house: Peter, John, James, Andrew, Philip, Thomas, Bartholomew, Matthew, James, son of Alphaeus, Simon the Zealot, Judas, son of James. They agreed to remain there, united in prayer, including the women. Jesus' mother Mary and his brothers were also there. 

In Judas' Place 

While they were there, about 120 people, Peter began to tell them, "Friends, long ago the Holy Spirit spoke through David about Judas, who became the guide of those who arrested Jesus. The Scriptures had to be fulfilled. Judas was one of us and had a designated place in this ministry. You know he took that damn bribe, bought a little plot of land, and had a tragic end: his belly ripped open and his guts spilled out. Everyone in Jerusalem knows that and they call him Meadow place of Murder. It's as we read in the Psalms: Let your place be deserted, so that no one lives there. And also what was written after: Let another take your place. Judas must have a substitute. Must be one of our group , someone who has been with us from the time Jesus was baptized by John until the day of his ascension, being also a witness of his resurrection." 

They indicated two names: José Barsabbas, nicknamed Justo, and Matthias. Then they prayed, "O God, you know each one of us, inside. Show us which of these two you choose to take in this leadership ministry the place that Judas left to go his own way." After praying, they drew lots. Matthias was chosen and joined the eleven apostles. 

(‎Acts of the Apostles 1)