Judas's office was filled by Matthias (Acts 1:16-26). The apostle Peter said, "For it is written in the Book of Psalms: 'Let his dwelling place be desolate, and let no one live in it'; and, 'Let another take his office'" (v. 20). Matthias was selected because he had been with Jesus and the other apostles "from the baptism of John to that day when He was taken up from us" (v. 22).
