I've pondered this word many times. It also has a singular/universal/variant side.
As the Catholic Church says, "It is right and it is just..." where "just" is used to imply law and legality, similar to justice. This form of "just" applies a meaning that it includes all people, therefore universal.
"I just want to kiss." Here it means only me, I am the only one who wants something and the thing I want is only a kiss.
Then there are others, "just in time", which is neither universal or singular but in this case it's an approximation to a specific time.
Just recently I noticed that just this law is not just onto Bedouins and their herds.