Peter said Judas’s place needed to be filled and described qualifications for someone who had accompanied them during Jesus’s ministry and become a witness to the resurrection (Acts 1:21–22). After prayer, they cast lots, and the lot fell on Matthias (Acts 1:24–26).
This episode occurs after Jesus’ departure and before the Pentecost scene in Acts 2.
This passage matters because it ties the detail to the larger movement of the book, keeping the answer connected to context rather than isolated wording.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Acts 1:21-22, then read the surrounding section so the answer stays connected to the passage's flow.
21Of the men therefore who have accompanied us all the time that the Lord Jesus went in and went out among us,
22beginning from the baptism of John, to the day that he was received up from us, of these must one become a witness with us of his resurrection."