Catechism of the Catholic Church

763 It was the Son's task to accomplish the Father's plan of salvation in the fullness of time. Its accomplishment was the reason for his being sent. ¹⁶⁰ "The Lord Jesus inaugurated his Church by preaching the Good News, that is, the coming of the Reign of God, promised over the ages in the scriptures." ¹⁶¹ To fulfill the Father's will, Christ ushered in the Kingdom of heaven on earth. The Church "is the Reign of Christ already present in mystery." ¹⁶²

764 "This Kingdom shines out before men in the word, in the works and in the presence of Christ." ¹⁶³ To welcome Jesus' word is to welcome "the Kingdom itself." ¹⁶⁴ The seed and beginning of the Kingdom are the "little flock" of those whom Jesus came to gather around him, the flock whose shepherd he is. ¹⁶⁵ They form Jesus' true family. ¹⁶⁶ To those whom he thus gathered around him, he taught a new "way of acting" and a prayer of their own. ¹⁶⁷

765 The Lord Jesus endowed his community with a structure that will remain until the Kingdom is fully achieved. Before all else there is the choice of the Twelve with Peter as their head. ¹⁶⁸ Representing the twelve tribes of Israel, they are the foundation stones of the new Jerusalem. ¹⁶⁹ The Twelve and the other disciples share in Christ's mission and his power, but also in his lot. ¹⁷⁰ By all his actions, Christ prepares and builds his Church.

766 The Church is born primarily of Christ's total self-giving for our salvation, anticipated in the institution of the Eucharist and fulfilled on the cross. "The origin and growth of the Church are symbolized by the blood and water which flowed from the open side of the crucified Jesus." ¹⁷¹ "For it was from the side of Christ as he slept the sleep of death upon the cross that there came forth the 'wondrous sacrament of the whole Church.'" ¹⁷² As Eve was formed from the sleeping Adam's side, so the Church was born from the pierced heart of Christ hanging dead on the cross. ¹⁷³