The recurring theme in the articles of this question is a re-emphasis that law is for the common good. It must serve a multitude of people, procure the common good by many actions and be intended to last from generation to generation. This requires a degree of generality which elicits some comments from Thomas:

1. Law is not meant to be applicable to particular cases. Does this introduce some uncertainty? Not to worry says Thomas and quotes Aristotle: "We must not seek the same degree of certainty in all things" (Nicomachean Ethics i, 3).
2. It does not pertain to human law to repress all vices but only those which disturb the common good: vices that hurt others "without the prohibition of which human society could not be maintained." (Article 2)
3. Nor does it pertain to human law to require all the acts of all the virtues but only those acts directed to the common good.
4. The just law binds in conscience.

The just law binds in conscience, but what is an unjust law to which my conscience is not bound? An unjust law is one which is contrary either to human or Divine good:

A human law is contrary to human good if it is:

1. not on the order of reason (I II 95.3), i.e. not ordained to the proper end, the common good,
2. not clearly expressed, i.e. incomprehensible, in which case harm ensues from the law itself,
3. ordained to private benefit, namely the ruler's,
4. imposes burdens unevenly.

A human law is contrary to Divine good if it is contrary to either the natural law or the Divine positive law. In our times such laws rarely require acts such as idolatory. More often the human law allows acts which are contrary to the Divine good but do not demand action, such as laws allowing homosexual marriages. These are not just laws: they are opposed to both the Divine good and the common good and "as Augustine says (De Lib. Arb. i, 5) 'a law that is not just, seems to be no law at all'" (Article 4).