c. Proof of the Third Main Conclusion

38. Proof of the third main conclusion [n.9] as follows: no persons would obligate themselves, at least not commonly, to so difficult an obligation unless there were some stricture in place, either a law of nature or a divine or human positive law. Every other licit contract is instituted or at least approved by law, because the correctness of such a contract or obligation is not a practical principle. So there is requirement that the rightness of this sort of contract be approved as a right obligation, or that this sort of contract be instituted or perceived as right.

39. But the law of nature, although it does obligate to the indissolubility of the aforesaid bond on the premise of such contract, is however not a very evident law of nature but is said in a secondary way. And what belongs to the law of nature only in a secondary way is not manifest to everyone. Therefore, it is expedient for the necessity of the precept to be determined by positive law.

40. But no legislator is above the whole of the human species save God alone; therefore it is expedient that the precept be approved or instituted or prescribed by the legislator who is God. For those things that are remote from the practical principles of the law of nature are not apparent to everyone in the way the practical principles are that are known to everyone, because they are not explicated and because other legislators do not know how to explicate such things. Therefore, it is expedient to explicate them through him who is universal Legislator over human nature.

41. Let it be too that a precept of the law of nature said in the primary way (namely a manifest practical principle or conclusion) would have obligated for this purpose; still it would be expedient for a divine precept to be set down for it, because men obey less the law alone of nature than they do God giving a precept, because they fear and revere their own consciences less than they do divine authority.

42. Nor is it expedient that this determination be done in the first way by the human positive law, because human positive laws vary among diverse peoples, and this indissolubility should be uniform among all.

43. Now this was done in Genesis 2.24 and Matthew 19.4, where Christ relates that God said what Adam pronounced in Genesis 2.24 [“man and wife shall be one flesh”], because God spoke through the mouth of Adam as of a herald; and     therefore Christ adds that God has united (supply: male and female) in a matrimonial union by the precept by which he pronounced it through the mouth of Adam, “a man shall cleave to his wife etc     .”

44. But one needs to understand that to prescribe the contract is one thing, and to prescribe perpetual cleaving on the premise of the contract is another.

For it was expedient for the first to be prescribed for the time for which there was a necessity of propagation, and especially if men were troublesome with respect to it without a precept. But for another time, for which there is no necessity, it has no need to be prescribed. Therefore, after the Fall God gave the precept twice about making the contract, first in Genesis 2.24, and again, when men had been destroyed by the Flood, in Genesis 9.1, 7.

But it is expedient for the second precept to be given for all time, because it was shown, in the first conclusion [nn.7, 12-13] that the indissolubility is consonant with the law of nature, and it will be less preserved unless, over and above this, there is a precept.

45. For this conclusion there is set down the following sort of reason: no one can obligate some owner’s property to owneer lord save by the consent and approval of him whose it is; but the body of anyone belongs by right of creation to God; therefore no one can transfer it to the ownership of another save insofar as God approves. Therefore, if the transfer is honorable for this end (as is plain from the first and second main conclusions [nn.7-8]), it follows that it is fitting that God approves this transfer of bodies.

46. But it would be said here that although a man be bound to God by creation in everything he can do, yet God does not exact so much of man; rather he freely leaves him to himself, demanding of him only that he keep the precepts of the Decalogue. Hence one can indeed sell oneself into slavery (although there is no special approval of this found in Scripture), in which selling one transfers ownership and power of one’s body to another as one does in the contracting of matrimony; the like is plain about the transfer of ownership of all one’s property. And the whole reason is because that in which God does not obligate a man or what is his own he leaves to man’s will.