Verba Tua manent in aeternum

Quas Primas, Encyclical of Pope Pius XI on the Feast of Christ the King (December 11th, 1925): 

24. (...) The feast of the Kingship of Christ, which in future will be yearly observed, may hasten the return of society to our loving Savior. It would be the duty of Catholics to do all they can to bring about this happy result. Many of these, however, have neither the station in society nor the authority which should belong to those who bear the torch of truth. This state of things may perhaps be attributed to a certain slowness and timidity in good people, who are reluctant to engage in conflict or oppose but a weak resistance; thus the enemies of the Church become bolder in their attacks. But if the faithful were generally to understand that it behooves them ever to fight courageously under the banner of Christ their King, then, fired with apostolic zeal, they would strive to win over to their Lord those hearts that are bitter and estranged from him, and would valiantly defend his rights.

25. Moreover, the annual and universal celebration of the feast of the Kingship of Christ will draw attention to the evils which anticlericalism has brought upon society in drawing men away from Christ, and will also do much to remedy them. While nations insult the beloved name of our Redeemer by suppressing all mention of it in their conferences and parliaments, we must all the more loudly proclaim his kingly dignity and power, all the more universally affirm his rights.