39 But, venerable brethren, it behooves us to strive by all means to preserve this divine union and render it ever more intimate and cordial, fixing our gaze not on human considerations but on those that are divine, in order that we may be all one thing alone in Christ. By developing this noble effort we shall fulfill ever better our sublime mission which is that of continuing and propagating the work of Christ, and of His Kingdom on earth. This, indeed, is why the Church throughout the ages continues to repeat the loving prayer, which is also the warmest aspiration of Our heart: "Holy Father, keep them in thy name, whom thou hast given me, that they may be one, as we also are" ( Ioan . xvii. 11).
Source: Communium Rerum (Vatican.va)