98 The ecumenical movement in our century, more than the ecumenical undertakings of past centuries, the importance of which must not however be underestimated, has been characterized by a missionary outlook. In the verse of John's Gospel which is ecumenism's inspiration and guiding motif—"that they may all be one ... so that the world may believe that you have sent me" ( Jn 17:21)—the phrase that the world may believe has been so strongly emphasized that at times we run the risk of forgetting that, in the mind of the Evangelist, unity is above all for the glory of the Father. At the same time it is obvious that the lack of unity among Christians contradicts the Truth which Christians have the mission to spread and, consequently, it gravely damages their witness. This was clearly understood and expressed by my Predecessor Pope Paul VI, in his Apostolic Exhortation Evangelii Nuntiandi : "As evangelizers, we must offer Christ's faithful not the image of people divided and separated by unedifying quarrels, but the image of people who are mature in faith and capable of finding a meeting-point beyond the real tensions, thanks to a shared, sincere and disinterested search for truth. Yes, the destiny of evangelization is certainly bound up with the witness of unity given by the Church ... At this point we wish to emphasize the sign of unity among all Christians as the way and instrument of evangelization. The division among Christians is a serious reality which impedes the very work of Christ". How indeed can we proclaim the Gospel of reconciliation without at the same time being committed to working for reconciliation between Christians? However true it is that the Church, by the prompting of the Holy Spirit and with the promise of indefectibility, has preached and still preaches the Gospel to all nations, it is also true that she must face the difficulties which derive from the lack of unity. When non-believers meet missionaries who do not agree among themselves, even though they all appeal to Christ, will they be in a position to receive the true message? Will they not think that the Gospel is a cause of division, despite the fact that it is presented as the fundamental law of love?
Source: Ut Unum Sint (Vatican.va)