19 Nevertheless, the naturalists,(32) as well as all who profess that they worship above all things the divinity of the State, and strive to disturb whole communities with such wicked doctrines, cannot escape the charge of delusion. Marriage has God for its Author, and was from the very beginning a kind of foreshadowing of the Incarnation of His Son; and therefore there abides in it a something holy and religious; not extraneous, but innate; not derived from men, but implanted by nature. Innocent III, therefore, and Honorius III, our predecessors, affirmed not falsely nor rashly that a sacrament of marriage existed ever amongst the faithful and unbelievers.(33) We call to witness the monuments of antiquity, as also the manners and customs of those people who, being the most civilized, had the greatest knowledge of law and equity. In the minds of all of them it was a fixed and foregone conclusion that, when marriage was thought of, it was thought of as conjoined with religion and holiness. Hence, among those, marriages were commonly celebrated with religious ceremonies, under the authority of pontiffs, and with the ministry of priests. So mighty, even in the souls ignorant of heavenly doctrine, was the force of nature, of the remembrance of their origin, and of the conscience of the human race. As, then, marriage is holy by its own power, in its own nature, and of itself, it ought not to be regulated and administered by the will of civil rulers, but by the divine authority of the Church, which alone in sacred matters professes the office of teaching.
Source: Arcanum Divinae (Vatican.va)