13 Nor are We unaware, Venerable Brethren, that in this fight for our altars we must also use all the legitimate human arms which are ready to our hands. For this reason, in Our Encyclical Letter Quadragesimo anno, following in the footsteps of Our predecessor, Leo XIII of illustrious memory, We contended so strenuously for a more equal division of earthly goods, indicating all those things by which the health and vigor of all human society may be most efficaciously restored, and peace and tranquillity may be given to its laboring members. For since a most vehement desire of obtaining a certain honorable happiness, even on this earth, has been implanted by the Maker of all things in the minds of mortal men, the Christian law has ever regarded with benevolence and actively fostered all legitimate efforts to promote the progress of true science, and to lead men by the right path to a higher condition.
Source: Caritate Christi Compulsi (Vatican.va)