Il Fermo Proposito §14

¹⁴ In order that this social action may continue and prosper by a necessary union of the various activities comprising it, Catholics above all must preserve a spirit of peace and harmony which can come only from a unity in understanding. On this point there cannot exist the least shadow or peradventure of a doubt, so clear and obvious are the teachings handed down by this Apostolic See, so brilliant is the light which most illustrious Catholics of every country have spread by their writings, so praiseworthy is the example of Catholics of other countries who, because of this harmony and unity of understanding, in a short time have reaped an abundant harvest.