49 It is, therefore, a fact which cannot be questioned that the true peace of Christ can only exist in the Kingdom of Christ - "the peace of Christ in the Kingdom of Christ." It is no less unquestionable that, in doing all we can to bring about the re-establishment of Christ's kingdom, we will be working most effectively toward a lasting world peace. Pius X in taking as his motto "To restore all things in Christ" was inspired from on High to lay the foundations of that "work of peace" which became the program and principal task of Benedict XV. These two programs of Our Predecessors We desire to unite in one - the re-establishment of the Kingdom of Christ by peace in Christ - "the peace of Christ in the Kingdom of Christ." With might and main We shall ever strive to bring about this peace, putting Our trust in God, Who when He called Us to the Chair of Peter, promised that the divine assistance would never fail Us. We ask that all assist and co-operate with Us in this Our mission. Particularly We ask you to aid us, Venerable Brothers, you, His sheep, whom Our leader and Lord, Jesus Christ, has called to feed and to watch over as the most precious portion of His flock, which comprises all mankind. For, it is you whom the "Holy Ghost hath placed to rule the Church of God" ( Acts xx, 28), you to whom above all, and principally, God "hath given the ministry of reconciliation, and who for Christ therefore are ambassadors." (II Cor . v, 18, 20) You participate in His teaching power and are "the dispensers of the mysteries of God." (I Cor. iv, 1) You have been called by Him "the salt of the earth," "the light of the world" ( Matt. v, 13, 14), fathers and teachers of Christian peoples, "a pattern of the flock from the heart" (I Peter v, 3), and "you shall be called great in the kingdom of heaven." ( Matt . v, 19) In fine, you are the links of gold, as it were, by which "the whole body of Christ, which is the Church, is held compacted and fitly joined together" ( Ephesians iv, 15, 16), built as it is on the solid rock of Peter.
Source: Ubi Arcano Dei Consilio (Vatican.va)