142 It is chiefly your duty, Venerable Brethren, and of your clergy, to search diligently for these lay apostles both of workers and of employers, to select them with prudence, and to train and instruct them properly. A difficult task, certainly, is thus imposed on priests, and to meet it, all who are growing up as the hope of the Church, must be duly prepared by an intensive study of the social question. Especially is it necessary that those whom you intend to assign in particular to this work should demonstrate that they are men possessed of the keenest sense of justice, who will resist with true manly courage the dishonest demands or the unjust acts of anyone, who will excel in the prudence and judgment which avoids every extreme, and, above all, who will be deeply permeated by the charity of Christ, which alone has the power to subdue firmly but gently the hearts and wills of men to the laws of justice and equity. Upon this road so often tried by happy experience, there is no reason why we should hesitate to go forward with all speed.
Source: Quadragesimo Anno (Vatican.va)