35 From these pronouncements of the Popes it is evident that the origin of public power is to be sought for in God Himself, and not in the multitude, and that it is repugnant to reason to allow free scope for sedition. Again, that it is not lawful for the State, any more than for the individual, either to disregard all religious duties or to hold in equal favour different kinds of religion; that the unrestrained freedom of thinking and of openly making known one's thoughts is not inherent in the rights of citizens, and is by no means to be reckoned worthy of favour and support. In like manner it is to be understood that the Church no less than the State itself is a society perfect in its own nature and its own right, and that those who exercise sovereignty ought not so to act as to compel the Church to become subservient or subject to them, or to hamper her liberty in the management of her own affairs, or to despoil her in any way of the other privileges conferred upon her by Jesus Christ. In matters, however, of mixed jurisdiction, it is in the highest degree consonant to nature, as also to the designs of God, that so far from one of the powers separating itself from the other, or still less coming into conflict with it, complete harmony, such as is suited to the end for which each power exists, should be preserved between them.
Source: Immortale Dei (Vatican.va)