Saint Matthias: "Become with us a witness"

Therefore, it is necessary that one of the men who accompanied us the whole time the Lord Jesus came and went among us, beginning from the baptism of John until the day on which he was taken up from us, become with us a witness to his resurrection." So they proposed two, Joseph called Barsabbas, who was also known as Justus, and Matthias.

-- Acts 1:15-17, 20-26

Everything that happened during those Paschal days involves each of the apostles - and Peter in particular - in the building of the new era begun on Easter morning. As witnesses of the Risen One, they remain the foundation stones of his Church. The faith of the first community of believers is based on the witness of concrete men known to the Christians and for the most part still living among them. Peter and the Twelve are the primary "witnesses to his Resurrection", but they are not the only ones - Paul speaks clearly of more than five hundred persons to whom Jesus appeared on a single occasion and also of James and of all the apostles.

-- CCC 642

Thus the risen Christ, by giving the Holy Spirit to the apostles, entrusted to them his power of sanctifying: they became sacramental signs of Christ. By the power of the same Holy Spirit they entrusted this power to their successors. This "apostolic succession" structures the whole liturgical life of the Church and is itself sacramental, handed on by the sacrament of Holy Orders.

-- CCC 1087