Is there just a single divine law?

It seems that there is just a single divine law:

Objection 1:  A single king in a single kingdom has a single law.  But the whole human race is related to God as to a single king—this according to Psalm 46:8 (“God is king of all the earth”).  Therefore, there is just a single divine law.

Objection 2:  Every law is ordered toward the end that the lawmaker intends in those for whom he makes the law.  But what God intends in all men is one and the same thing—this according to 1 Timothy 2:4 (“He wills that all men be saved and come to knowledge of the truth”).  Therefore, there is just a single divine law.

Objection 3:  Divine law seems to be closer to eternal law, which is a single law, than is natural law, to the extent that the revelation of grace is higher than natural cognition.  But natural law is a single law for all men.  Therefore, a fortiori, so is divine law.

But contrary to this:  In Hebrews 7:12 the Apostle says, “For the priesthood having been changed, it is necessary for the law to be changed.”  But as is explained in the same place, there are two kinds of priesthood, the Levitical priesthood and Christ’s priesthood.  Therefore, there are two laws, viz., the Old Law and the New Law.

I respond:  As was explained in the First Part (ST 1, q. 30, a. 3), distinction is a cause of number.  Now there are two ways in which things can be distinct from one another.  First, they are distinct in the sense of being altogether diverse in species, e.g., a horse and an ox.  Second, they are distinct in the sense that the one is perfect and the other imperfect within the same species, e.g., a man and a boy.  It is in this latter sense that the divine law is divided into the Old Law and the New Law.  Hence, in Galatians 3:24‑25, the Apostle compares the status of the Old Law to the status of a child under the tutelage of a pedagogue, while he compares the status of the New Law to a full‑grown man who is no longer under the tutelage of a pedagogue.
Now perfection and imperfection apply to these laws with respect to three aspects relevant to law that were noted above.
First, as was noted above (q. 90, a. 2), law is ordered toward the common good as its end.  But there are two kinds of common good.  The first is a sensible and earthly good, and it is to this good that the Old Law immediately ordered [the people]; hence, in Exodus 3:8‑17, at the very initiation of the Old Law, the people are invited into the earthly kingdom of the Canaanites.  The second is an intelligible and heavenly good, and it is to this good that the New Law orders [the people]; hence, at the very beginning of His teaching Christ issued an invitation to the kingdom of heaven, saying, “Repent, for the kingdom of heaven is at hand” (Matthew 4:17).  Thus, in Contra Faustum 4 Augustine says, “Promises of temporal things were contained in the Old Testament, and this is why it is called ‘Old’; by contrast, the New Testament has to do with the promise of eternal life.”
Second, law has to do with directing human acts in accord with the order of justice.  On this score, too, the New Law outstrips the Old Law by ordering the interior acts of the soul—this according to Matthew 5:20, “Unless your justice exceeds that of the Scribes and Pharisees, you will not enter into the kingdom of heaven.”  For this reason it is said that the Old Law restrains the hand, whereas the New Law restrains the mind.
Third, law has the role of inducing men to the obey the commandments.  The Old Law did this through the fear of punishment, whereas the New Law does it through the love that is infused into our hearts through Christ’s grace, which is conferred under the New Law but was prefigured under the Old Law.  This is why in Contra Adimantum Manichaei Discipulum Augustine says, “In short, the difference between the Law and the Gospel is this:  fear and love.”

Reply to objection 1:  Just as the father of a household issues different commands to children and to adults, so too the one king God, within His single kingdom, gives one law to men who are still imperfect and another more perfect law to those who have already been led by the hand through the prior law to a greater capacity for divine things.

Reply to objection 2:  The salvation of men was impossible except through Christ—this according to Acts 4:12 (“There is no other name given to men, whereby we must be saved”).  And so a law that leads all men perfectly to salvation could not have been given prior to Christ’s coming.  Before that, the people from whom Christ was to be born had to be given a preparatory law for receiving Christ, and in this law certain rudiments of salvific justice were contained.

Reply to objection 3:  The natural law directs man in accord with certain general precepts which are shared by both perfect and imperfect men, and this is why there is a single natural law for everyone.  In addition, however, the divine law directs man in certain particulars with respect to which the perfect and the imperfect are not similarly positioned.  And this is why, as has already been explained, it was necessary for there to be two divine laws.