Objection 1. It would seem that the precepts of the virtues annexed to temperance are unsuitably given in the Divine law. For the precepts of the Decalogue, as stated above (1, ad 3), are certain universal principles of the whole Divine law. Now "pride is the beginning of all sin," according to Sirach 10:15. Therefore among the precepts of the Decalogue there should have been one forbidding pride.
Objection 2. Further, a place before all should have been given in the decalogue to those precepts by which men are especially induced to fulfil the Law, because these would seem to be the most important. Now since humility subjects man to God, it would seem most of all to dispose man to the fulfilment of the Divine law; wherefore obedience is accounted one of the degrees of humility, as stated above (Question 161, Article 6); and the same apparently applies to meekness, the effect of which is that a man does not contradict the Divine Scriptures, as Augustine observes (De Doctr. Christ. ii, 7). Therefore it seems that the Decalogue should have contained precepts of humility and meekness.
Objection 3. Further, it was stated in the foregoing Article that adultery is forbidden in the decalogue, because it is contrary to the love of our neighbor. But inordinateness of outward movements, which is contrary to modesty, is opposed to neighborly love: wherefore Augustine says in his Rule (Ep. ccxii): "In all your movements let nothing be done to offend the eye of any person whatever." Therefore it seems that this kind of inordinateness should also have been forbidden by a precept of the Decalogue.
On the contrary, suffices the authority of Scripture.
I answer that, The virtues annexed to temperance may be considered in two ways: first, in themselves; secondly, in their effects. Considered in themselves they have no direct connection with the love of God or of our neighbor; rather do they regard a certain moderation of things pertaining to man himself. But considered in their effects, they may regard the love of God or of our neighbor: and in this respect the decalogue contains precepts that relate to the prohibition of the effects of the vices opposed to the parts of temperance. Thus the effect of anger, which is opposed to meekness, is sometimes that a man goes on to commit murder (and this is forbidden in the Decalogue), and sometimes that he refuses due honor to his parents, which may also be the result of pride, which leads many to transgress the precepts of the first table.
Reply to Objection 1. Pride is the beginning of sin, but it lies hidden in the heart; and its inordinateness is not perceived by all in common. Hence there was no place for its prohibition among the precepts of the Decalogue, which are like first self-evident principles.
Reply to Objection 2. Those precepts which are essentially an inducement to the observance of the Law presuppose the Law to be already given, wherefore they cannot be first precepts of the Law so as to have a place in the Decalogue.
Reply to Objection 3. Inordinate outward movement is not injurious to one's neighbor, if we consider the species of the act, as are murder, adultery, and theft, which are forbidden in the decalogue; but only as being signs of an inward inordinateness, as stated above (168, 1, ad 1,3).
Source: Summa Theologica (New Advent)