25 In addition to what has been laid down, it is necessary to enter more fully into the nature of the Church. She is not an association of Christians brought together by chance, but is a divinely established and admirably constituted society, having for its direct and proximate purpose to lead the world to peace and holiness. And since the Church alone has, through the grace of God, received the means necessary to realize such end, she has her fixed laws, special spheres of action, and a certain method, fixed and conformable to her nature, of governing Christian peoples. But the exercise of such governing power is difficult, and leaves room for numberless conflicts, inasmuch as the Church rules peoples scattered through every portion of the earth, differing in race and customs, who, living under the sway of the laws of their respective countries, owe obedience alike to the civil and religious authorities. The duties enjoined are incumbent on the same persons, as already stated, and between them there exists neither contradiction nor confusion; for some of these duties have relation to the prosperity of the State, others refer to the general good of the Church, and both have as their object to train men to perfection.
Source: Sapientiae Christianae (Vatican.va)