8. From these considerations finally it is concluded that no king or monarch has or has had directly from God or from divine institution a political principality, but by the medium of human will and institution. This is the honored axiom of theology, not for derision, as the king proposed, but in truth, because rightly understood it is most true and especially necessary for understanding the purposes and limits of civil power.
St. Thomas insinuates it in Ia IIae, q.9 a.3.
9. Besides this truth can be taken from the holy Fathers, first, because they assert that man was created by God free and free-born, and only received directly from God the power of ruling over the brute beasts and inferior things; but the dominion of men over men was introduced by human will through sin or some adversity. This Ambrose hands down on Colossians 3, at the end; and more broadly Augustine, 19, The City of God, ch.15, and bk. Quaestion. in Gen. q.153, and Gregory bk.21, Moralia, ch.10, elsewhere ch.11, and in Pastorali, p.2, ch.6.
For what they say about the liberty of each man, and the slavery opposed to it, is by the same reasoning true of a mixed or fictitious person of a single community or human city. For, according as it is directly ruled by God with the law of nature, it is free and sui iuris. This liberty does not exclude, but rather includes, the power of ruling itself, and of giving commands to its own members, but it excludes subjection to another man, as far as it is by force of natural law alone, because God has given directly such power to no one among men until through human institution or election it be transferred to someone. Secondly, this is particularly confirmed by the opinion of Augustine, bk.3, Confessions, ch.8, where he says: “It is a general pact of human society to obey its own kings.” For by these words he signifies that the regal principality, and the obedience owed to it, has its basis in a pact of human society, and therefore it is not from the direct institution of God, for a human pact is contracted by human will.
But this power of which we are treating was given by none of these methods to kings by God, speaking according to the ordinary law, because neither through the special will of God was it directly given, nor also does the natural law alone dictate by itself that this power should be in kings, as has been shown; lastly, the institution, or determination, or transfer of this power was not made directly by God to the kings, as is plain from experience itself…