11 Let the Princes and Rulers of peoples remember this truth, and let them consider whether it is a prudent and safe idea for governments or for states to separate themselves from the holy religion of Jesus Christ, from which their authority receives such strength and support. Let them consider again and again, whether it is a measure of political wisdom to seek to divorce the teaching of the Gospel and of the Church from the ruling of a country and from the public education of the young. Sad experience proves that human authority fails where religion is set aside. The fate of our first parent after the Fall is wont to come also upon nations. As in his case, no sooner had his will turned from God than his unchained passions rejected the sway of the will; so, too, when the rulers of nations despise divine authority, in their turn the people are wont to despise their human authority. There remains, of course, the expedient of using force to repress popular risings; but what is the result? Force can repress the body, but it cannot repress the souls of men.
Source: Ad Beatissimi Apostolorum (Vatican.va)