Soon after the Ascension of Christ, the eleven remaining apostles gathered to choose someone to replace Judas Iscariot. St. Peter lays out the qualifications needed for an apostle: he must be “one of the men who have accompanied us during all the time that the Lord Jesus went in and out among us, beginning from the baptism of John until the day when he was taken up from us” (Acts 1:21-22). But why was another apostle needed? What would this new apostle be doing? Peter tells us: he “must become with us a witness to his resurrection” (Acts 1:22).
“A witness to his resurrection.” Even before the outpouring of the Holy Spirit at Pentecost, the first followers of Jesus understood their primary mission was to tell others about his miraculous Resurrection from the dead and what it means for us. On Pentecost, the Holy Spirit confirms this mission and makes their witness more powerful. In the first Christian sermon (Acts 2:14-36), Peter makes the Resurrection the central theme of his preaching.