30 Our own time, with humanity on the move and in continual search, demands a resurgence of the Church's missionary activity . The horizons and possibilities for mission are growing ever wider, and we Christians are called to an apostolic courage based upon trust in the Spirit. He is the principal agent of mission! The history of humanity has known many major turning points which have encouraged missionary outreach, and the Church, guided by the Spirit, has always responded to them with generosity and farsightedness. Results have not been lacking. Not long ago we celebrated the millennium of the evangelization of Rus' and the Slav peoples, and we are now preparing to celebrate the five hundredth anniversary of the evangelization of the Americas. Similarly, there have been recent commemorations of the centenaries of the first missions in various countries of Asia, Africa and Oceania. Today the Church must face other challenges and push forward to new frontiers, both in the initial mission ad gentes and in the new evangelization of those peoples who have already heard Christ proclaimed. Today all Christians, the particular churches and the universal Church, are called to have the same courage that inspired the missionaries of the past, and the same readiness to listen to the voice of the Spirit.
Source: Redemptoris Missio (Vatican.va)