No oppression is so heavy or lasting as that which is inflicted by the perversion and exorbitance of legal authority.

The saying warns that the most enduring form of tyranny is not open violence but the corruption of law itself. When legal authority is “perverted” (turned from its proper ends) and becomes “exorbitant” (overreaching its limits), oppression gains the appearance of legitimacy: it can be administered routinely, defended as procedure, and made difficult to resist because it is cloaked in the language of justice. The quote thus distinguishes between power and lawful power, arguing that abuses committed under color of law are especially heavy because they enlist institutions meant to protect citizens and convert them into instruments of domination.