28 If the practical solution depends on concrete circumstances, We must, however, on Our part recall to you some general principles, always to be kept in mind, and they are: 1) That these revindications have reason [the ratio] of means, or of relative end, not of ultimate and absolute end; 2) That, in reason [ratio] of means, they must be licit actions and not intrinsically evil; 3) That, if they are to be means proportionate to the end, they must be used only in the measure in which they serve to obtain or render possible, in whole or in part, the end, and in such manner that they do not cause to the community greater damages than those they seek to repair; 4) That the use of such means and the exercise of civic and political rights in their fulness, embracing also problems of order purely material and technical, or any violent defense, does not enter in any manner in the task of the clergy or of Catholic Action as such, although to both appertains the preparation of Catholics to make just use of their rights, and to defend them with all legitimate means according as the common good requires; 5) The clergy and Catholic Action, being, by their mission of peace and love, consecrated to uniting all men in vinculo pacis ( Ephesians iv. 3), must contribute to the prosperity of the nation, especially encouraging the union of those social initiatives which are not opposed to dogma or to the laws of Christian morals. Furthermore, this very civil activity of the Mexican Catholics, carried out with such a noble and elevated spirit, will obtain results that are the more efficacious the more the Catholics themselves shall have the supernatural vision of life, that religious and moral education and that burning zeal for the spread of the Kingdom of Our Lord Jesus Christ which Catholic Action intends to give.
Source: Firmissimam Constantiam (Vatican.va)