In the first act of Measure for Measure, the line “There’s not a soldier of us all, that, in/the thanksgiving before meat, do relish the petition/well that prays for peace” stuck out as being a sort of summation of how the characters feel about the situation with Lord Angelo in charge (1.2.110-114).  Soldiers understand that they are not supposed to want to go to war, but they do not try to pray earnestly to prevent it because there is a part of them which enjoys warring.  The characters of the play understand that, as Christians, they are not supposed to desire or engage in extramarital sexual encounters, but their overwhelming want for such encounters make them disapprove of attempts to prevent it outright, or punish it so harshly.  Like the soldiers, they understand the way they are “supposed” to act and feel, but the reality of their situation is at odds with what is expected of them.  They see lechery as only a minor crime, much in the same way that we would view jaywalking.  Isabella understands that her brother can be put to death from a legal and even (in her strict, rigid, virginal opinion) moral standpoint, but she does not want him to die because she loves him in spite of his actions, and because he’s ultimately still a good person who engaged in a mutually consensual act.  There is a divide between what the laws say, and what we recognize as “virtuous,” with the realities of human behavior and desire.  This divide permeates both acts of the play, from Claudio and Juliet’s premarital sex, to the legality of the brothel, to Lord Angelo’s own blackmailing of Isabella.

Other than the moral argument itself about sex, the play evokes the longstanding dispute between de facto and de jure in lawmaking and governance, with de facto being the state of things in practice and de jure being the written laws themselves.  Vincentio is obviously upset by the fact that the de facto state of affairs is to ignore the de jure laws which were instilled.  The kinds of laws which are ignored so widely are said to be in a state of “desuetude.”  Lord Angelo is introduced to implement a Draconian, letter-of-the-law style of governance.  He resolves to make the law something more than just a “scarecrow” which is eventually used by its targets as a perch (2.1.4).