I wouldn't say natural law so much as people in the society generally agreeing to follow certain rules so that society can function and be stable.
If you had a society where everybody was allowed to kill anyone they didn't like, that society would fall apart quickly. If you had a society where people could steal from other people, that society wouldn't do very well.
Obviously not everybody follows all of the rules all of the time, and some societies have some bad rules, but generally speaking, if enough people follow the rules most the time, society can do pretty well.