Legislation is mostly about creating rules for how government should operate, rather than just making laws to follow. In England, for a long time, common law existed without being controlled by the government, which shows that legislatures were more focused on managing government functions. Their main job is to organize and direct government actions, including making sure justice is served.
Rules of just conduct, which keep society fair and orderly, can change over time and do not need to be created purposely. In contrast, the government needs specific rules that outline its roles and operations. These rules help establish commands and duties for different government agencies and create a system of authority.
Even when enforcing justice, there are rules for how the enforcement should happen, and these rules are different from the basic rules of just conduct. Rulers also needed to create general rules for governing, which often depended on what the public believed their powers to be. The need for legislative bodies became important for gaining public consent for things like taxes, leading to parliamentary institutions focused mainly on government management rather than just making laws. Over time, the rules for how government works gained authority similar to laws.