51 All that we have said so far regarding the activity of the State in educational matters, rests on the solid and immovable foundation of the Catholic doctrine of The Christian Constitution of States set forth in such masterly fashion by Our Predecessor Leo XIII, notably in the Encyclicals Immortale Dei and Sapientiae Christianae . He writes as follows: God has divided the government of the human race between two authorities, ecclesiastical and civil, establishing one over things divine, the other over things human. Both are supreme, each in its own domain; each has its own fixed boundaries which limit its activities. These boundaries are determined by the peculiar nature and the proximate end of each, and describe as it were a sphere within which, with exclusive right, each may develop its influence. As however the same subjects are under the two authorities, it may happen that the same matter, though from a different point of view, may come under the competence and jurisdiction of each of them. If follows that divine Providence, whence both authorities have their origin, must have traced with due order the proper line of action for each. The powers that are, are ordained of God.
Source: Divini Illius Magistri (Vatican.va)