58 Tell your faithful children of the laity that when, united with their pastors and their bishops, they participate in the works of the apostolate, both individual and social, the end purpose of which is to make Jesus Christ better known and better loved, then they are more than ever "a chosen generation, a kingly priesthood, a holy nation, a purchased people," of whom St. Peter spoke in such laudatory terms. (I Peter ii, 9) Then, too, they are more than ever united with Us and with Christ, and become great factors in bringing about world peace because they work for the restoration and spread of the Kingdom of Christ. Only in this Kingdom of Christ can we find that true human equality by which all men are ennobled and made great by the selfsame nobility and greatness, for each is ennobled by the precious blood of Christ. As for those who are in authority, they are, according to the example of our Lord Jesus Christ, but ministers of the good, servants of the servants of God, particularly of the sick and of those in need.
Source: Ubi Arcano Dei Consilio (Vatican.va)