Was it necessary for there to be such a thing as divine law?

It seems to have been unnecessary for there to be such a thing as divine law:

Objection 1:  As has been explained (a. 2), natural law is within us a kind of participation in eternal law.  But as has been said (a. 1), eternal law is a divine law.  Therefore, it is unnecessary for there to be a divine law in addition to natural law and the human laws that stem from it.

Objection 2:  Ecclesiasticus 15:14 says, “God left man in the hand of his own counsel.”  But as was established above (q., 14, a. 1), counsel is an act of reason.  Therefore, man was left to the governance provided by his own reason.  But as has been explained (a. 3), a dictate of human reason is human law.  Therefore, it is unnecessary for man to be governed by some other divine law.

Objection 3:  Human nature is more self-sufficient than non‑rational creatures.  But a non‑rational creature does not have any divine law in addition to the natural inclination that has been instilled in it.  Therefore, a fortiori, a rational creature should not have any divine law in addition to natural law.

But contrary to this:  David asked God for a law to be imposed on him, saying, “Set before me for a law the way of Your justifications, O Lord” (Psalm 118:33).

I respond:  In addition to natural law and human law, it was necessary for us to have divine law in order to direct human life—and this for four reasons:
First, through law man is directed to his own acts in relation to the ultimate end.  And if man were ordered just to an end that is not disproportionate to man’s natural power, then it would be unnecessary for man to have any directive from reason in addition to natural law and the humanly posited law that stems from it.  However, since, as was established above (q. 5, a. 5), man is ordered to the end of eternal beatitude, which is disproportionate to natural human power, it was necessary that, in addition to natural law and human law, he should also be directed to his end by a law that is divinely given.
Second, due to the uncertainty of human judgment, especially about contingent and particular matters, different people can make diverse judgments about human acts, and these diverse judgments lead to diverse and contrary laws.  Therefore, in order that man might be able to know without any hesitation what he should do and what he should avoid doing, it was necessary that he be directed in his proper acts by a law that is divinely given and is clearly such that it cannot be mistaken.
Third, man is able to make law with respect to those things which he is in a position to make judgments about.  But human judgments cannot encompass interior movements, which are hidden, but only exterior acts, which are observable.  Yet for the perfection of virtue it is required that a man be upright with respect to both sorts of acts.  So human law was unable to restrain and to order interior acts adequately, and divine law had to be added for this purpose.
Fourth, as Augustine says in De Libero Arbitrio 1, human law is incapable of prohibited or punishing all evil deeds.  For if it tried to do away with all evils, many goods would likewise be destroyed as a result, and the benefits of the common good, which is necessary for human living, would be impeded.  Therefore, in order that no evil would remain unforbidden and unpunished, it was necessary that there should be, in addition, a divine law by which all sins would be prohibited.
These four reasons are touched on in Psalm 18:8, where it says, “The law of the Lord is unspotted ....,” i.e., does not permit any foulness of sin; “..... converting souls ....,” since it directs not just exterior acts, but interior acts as well; “..... the testimony of the Lord is faithful .....,” because of the certitude of what is true and of upright; “..... giving wisdom to the little ones,” insofar as it orders man to his supernatural and divine end.

Reply to objection 1:  Natural law participates in eternal law in a way proportioned to the power of human nature.  But man has to be directed in a deeper way to his ultimate supernatural end.  And so there is, in addition, a divinely given law, through which eternal law is participated in more deeply.

Reply to objection 2:  Counsel is a certain sort of inquiry, and so it must proceed from given principles.  But it is not enough that it should proceed from naturally instilled principles, i.e., from the precepts of the natural law—and this for the [four] reasons explained above.  Rather, it is necessary that certain other principles should be added, viz., the precepts of divine law.

Reply to objection 3:  Non‑rational creatures are not ordered to a higher end than the end that is proportioned to their natural power.  And so the arguments are not parallel.