Objection 1. It would seem that the moral precepts of the Law are not about all the acts of virtue. For observance of the precepts of the Old Law is called justification, according to Psalm 118:8: "I will keep Thy justifications." But justification is the execution of justice. Therefore the moral precepts are only about acts of justice.
Objection 2. Further, that which comes under a precept has the character of a duty. But the character of duty belongs to justice alone and to none of the other virtues, for the proper act of justice consists in rendering to each one his due. Therefore the precepts of the moral law are not about the acts of the other virtues, but only about the acts of justice.
Objection 3. Further, every law is made for the common good, as Isidore says (Etym. v, 21). But of all the virtues justice alone regards the common good, as the Philosopher says (Ethic. v, 1). Therefore the moral precepts are only about the acts of justice.
On the contrary, Ambrose says (De Paradiso viii) that "a sin is a transgression of the Divine law, and a disobedience to the commandments of heaven." But there are sins contrary to all the acts of virtue. Therefore it belongs to Divine law to direct all the acts of virtue.
I answer that, Since the precepts of the Law are ordained to the common good, as stated above (Question 90, Article 2), the precepts of the Law must needs be diversified according to the various kinds of community: hence the Philosopher (Polit. iv, 1) teaches that the laws which are made in a state which is ruled by a king must be different from the laws of a state which is ruled by the people, or by a few powerful men in the state. Now human law is ordained for one kind of community, and the Divine law for another kind. Because human law is ordained for the civil community, implying mutual duties of man and his fellows: and men are ordained to one another by outward acts, whereby men live in communion with one another. This life in common of man with man pertains to justice, whose proper function consists in directing the human community. Wherefore human law makes precepts only about acts of justice; and if it commands acts of other virtues, this is only in so far as they assume the nature of justice, as the Philosopher explains (Ethic. v, 1).
But the community for which the Divine law is ordained, is that of men in relation to God, either in this life or in the life to come. And therefore the Divine law proposes precepts about all those matters whereby men are well ordered in their relations to God. Now man is united to God by his reason or mind, in which is God's image. Wherefore the Divine law proposes precepts about all those matters whereby human reason is well ordered. But this is effected by the acts of all the virtues: since the intellectual virtues set in good order the acts of the reason in themselves: while the moral virtues set in good order the acts of the reason in reference to the interior passions and exterior actions. It is therefore evident that the Divine law fittingly proposes precepts about the acts of all the virtues: yet so that certain matters, without which the order of virtue, which is the order of reason, cannot even exist, come under an obligation of precept; while other matters, which pertain to the well-being of perfect virtue, come under an admonition of counsel.
Reply to Objection 1. The fulfilment of the commandments of the Law, even of those which are about the acts of the other virtues, has the character of justification, inasmuch as it is just that man should obey God: or again, inasmuch as it is just that all that belongs to man should be subject to reason.
Reply to Objection 2. Justice properly so called regards the duty of one man to another: but all the other virtues regard the duty of the lower powers to reason. It is in relation to this latter duty that the Philosopher speaks (Ethic. v, 11) of a kind of metaphorical justice.
The Reply to the Third Objection is clear from what has been said about the different kinds of community.
Source: Summa Theologica (New Advent)