1 The mission of Christ the Redeemer, which is entrusted to the Church, is still very far from completion. As the second millennium after Christ's coming draws to an end, an overall view of the human race shows that this mission is still only beginning and that we must commit ourselves wholeheartedly to its service. It is the Spirit who impels us to proclaim the great works of God: "For if I preach the Gospel, that gives me no ground for boasting. For necessity is laid upon me. Woe to me if I do not preach the Gospel!" (1 Cor 9: 16) In the name of the whole Church, I sense an urgent duty to repeat this cry of St. Paul. From the beginning of my Pontificate I have chosen to travel to the ends of the earth in order to show this missionary concern. My direct contact with peoples who do not know Christ has convinced me even more of the urgency of missionary activity , a subject to which I am devoting the present encyclical. The Second Vatican Council sought to renew the Church's life and activity in the light of the needs of the contemporary world. The Council emphasized the Church's "missionary nature," basing it in a dynamic way on the Trinitarian mission itself. The missionary thrust therefore belongs to the very nature of the Christian life, and is also the inspiration behind ecumenism: "that they may all be one...so that the world may believe that you have sent me" (Jn 17:21).
Source: Redemptoris Missio (Vatican.va)