People today put more trust in witnesses than in teachers, in experience than in teaching, and in life and action than in theories. The witness of a Christian life is the first and irreplaceable form of mission: Christ, whose mission we continue, is the "witness" par excellence (Rv 1:5; 3:14) and the model of all Christian witness. The Holy Spirit accompanies the Church along her way and associates her with the witness he (the Holy Spirit)gives to Christ (cf. Jn 15:26-27).
The first form of witness is the very life of the missionary, of the Christian family, and of the ecclesial community, which reveal a new way of living. The missionary who, despite all his or her human limitations and defects, lives a simple life, taking Christ as the model, is a sign of God and of transcendent realities. But everyone in the Church, striving to imitate the Divine Master, can and must bear this kind of witness; in many cases it is the only possible way of being a missionary.
The evangelical witness which the world finds most appealing is that of concern for people, and of charity toward the poor, the weak and those who suffer. The complete generosity underlying this attitude and these actions stands in marked contrast to human selfishness. It raises precise questions which lead to God and to the Gospel. A commitment to peace, justice, human rights and human promotion is also a witness to the Gospel when it is a sign of concern for persons and is directed toward integral human development.
The Church is called to bear witness to Christ by taking courageous and prophetic stands in the face of the corruption of political or economic power; by not seeking her own glory and material wealth; by using her resources to serve the poorest of the poor and by imitating Christ's own simplicity of life. The Church and her missionaries must also bear the witness of humility, above all with regard to themselves—a humility which allows them to make a personal and communal examination of conscience in order to correct in their behavior whatever is contrary to the Gospel and disfigures the face of Christ.
St. John Paul II, encyclical letter
Redemptoris Missio, nn. 43 and 43