9 Meanwhile, in accordance with your office, give notice to the faithful of this our paternal invitation; recall to them once more from what principles a just and lasting peace may issue and by what means it must be sought. Indeed, as you well know, it can only be obtained from the principles and norms dictated by Christ and put into practice with sincere piety. Such principles and norms, in fact, recall men to truth, justice and charity; they put a restraint on their unruly desires; they force the senses to be obedient to reason; they move the reason to obey God; they produce this effect, that all men, even those who are rulers of the peoples, may recognize the freedom that is due to religion, which, beyond its primary purpose of leading souls to eternal salvation, has also another, of safeguarding and protecting the very foundations of the State.
Source: Summi Maeroris (Vatican.va)