43 In Our first Encyclical Letter, We already recalled various important reasons which make it imperative, in our time, to recruit in all parts of the world "the laity to the ranks of a peaceful militia, Catholic Action, so that the laity should cooperate in the apostolate of the hierarchy." (74) We commented on this with the following words: "It gives Us great comfort that, over the years, in lands that are still mission territories, these valuable aides to bishops and priests have worked so hard for the success of their projects." (75) And now, impelled "by the love of Christ," (76) We wish to renew urgently the exhortations and appeals of Our predecessor Pius XII: "It is necessary that laymen give their generous, zealous, and active cooperation, joining the clergy in their apostolic work and swelling to large numbers the ranks of Catholic Action." (77) The bishops of mission countries endeavored to do their best to carry out the directives of the Supreme Pontiff, together with the regular and religious clergy, and the most generous and well-trained laymen; We can state that splendid successes in this field are being achieved all over the earth.
Source: Princeps Pastorum (Vatican.va)