96 To achieve this latter lofty aim, and in particular to promote the common good truly and permanently, We hold it is first and above everything wholly necessary that God bless it and, secondly, that all men of good will work with united effort toward that end. We are further convinced, as a necessary consequence, that this end will be attained the more certainly the larger the number of those ready to contribute toward it their technical, occupational, and social knowledge and experience; and also, what is more important, the greater the contribution made thereto of Catholic principles and their application, not indeed by Catholic Action (which excludes strictly syndical or political activities from its scope) but by those sons of Ours whom Catholic Action imbues with Catholic principles and trains for carrying on an apostolate under the leadership and teaching guidance of the Church - of that Church which in this field also that We have described, as in every other field where moral questions are involved and discussed, can never forget or neglect through indifference its divinely imposed mandate to be vigilant and to teach.
Source: Quadragesimo Anno (Vatican.va)