Immortale Dei §13

¹³ The Almighty, therefore, has given the charge of the human race to two powers, the ecclesiastical and the civil, the one being set over divine, and the other over human, things. Each in its kind is supreme, each has fixed limits within which it is contained, limits which are defined by the nature and special object of the province of each, so that there is, we may say, an orbit traced out within which the action of each is brought into play by its own native right. But, inasmuch as each of these two powers has authority over the same subjects, and as it might come to pass that one and the same thing-related differently, but still remaining one and the same thing-might belong to the jurisdiction and determination of both, therefore God, who foresees all things, and who is the author of these two powers, has marked out the course of each in right correlation to the other. "For the powers that are, are ordained of God."!(17) Were this not so, deplorable contentions and conflicts would often arise, and, not infrequently, men, like travellers at the meeting of two roads, would hesitate in anxiety and doubt, not knowing what course to follow. Two powers would be commanding contrary things, and it would be a dereliction of duty to disobey either of the two.