19 The Lord Jesus, after praying to the Father, calling to Himself those whom He desired, appointed twelve to be with Him, and whom He would send to preach the Kingdom of God; and these apostles He formed after the manner of a college or a stable group, over which He placed Peter chosen from among them. He sent them first to the children of Israel and then to all nations, so that as sharers in His power they might make all peoples His disciples, and sanctify and govern them, and thus spread His Church, and by ministering to it under the guidance of the Lord, direct it all days even to the consummation of the world. And in this mission they were fully confirmed on the day of Pentecost in accordance with the Lord's promise: "You shall receive power when the Holy Spirit comes upon you, and you shall be witnesses for me in Jerusalem, and in all Judea and in Samaria, and even to the very ends of the earth". And the apostles, by preaching the Gospel everywhere, and it being accepted by their hearers under the influence of the Holy Spirit, gather together the universal Church, which the Lord established on the apostles and built upon blessed Peter, their chief, Christ Jesus Himself being the supreme cornerstone.(146)
Source: Lumen Gentium (Vatican.va)