Thomas Aquinas

“ From becoming accustomed to avoid evil and fulfill what is good, through fear of punishment, one is sometimes led on to do so likewise, with delight and of one's own accord. Accordingly, law, even by punishing, leads men on to being good. ”

“ Since then every man is a part of the state, it is impossible that a man be good, unless he be well proportionate to the common good: nor can the whole be well consistent unless its parts be proportionate to it. Consequently the common good of the state cannot flourish, unless the citizens be virtuous, at least those whose business it is to govern. ”

“ Some acts are evil generically, viz. acts of vice, and in respect of these the law forbids. Some acts are generically indifferent, and in respect of these the law permits; and all acts that are either not distinctly good or not distinctly bad may be called indifferent. And it is the fear of punishment that law makes use of in order to ensure obedience: in which respect punishment is an effect of law.
Reply to Objection 1: Just as to cease from evil is a kind of good, so a prohibition is a kind of precept: and accordingly, taking precept in a wide sense, every law is a kind of precept. ”