How we cite our quotes: Section.Part (if applicable).Paragraph
Quote #4
In general we may observe that all questions of property are subordinate to the authority of civil laws, which extend, restrain, modify, and alter the rules of natural justice, according to the particular convenience of each community. The laws have, or ought to have, a constant reference to the constitution of government, the manners, the climate, the religion, the commerce, the situation of each society. (III.II.13)
As well as the big, country-wide laws, communities can set up other rules that they find convenient. Still, we have to remember that communities exist within society rather than apart from it. This means that folks should keep in mind the government and the laws of society (rather than just doing whatever they please).
Quote #5
It may appear to a careless view, or rather a too abstracted reflection, that there enters a like superstition into all the sentiments of justice; and that, if a man expose its object, or what we call property, to the same scrutiny of sense and science, he will not [...] find any foundation for the difference made by moral sentiment. I may lawfully nourish myself from this tree; but the fruit of another of the same species, ten paces off, it is criminal for me to touch. The same species of reasoning it may be thought, which so successfully exposes superstition, is also applicable to justice. (III.II.16)
Justice and superstition may not seem to have much in common at first: one conjures up weird, mystical stuff while the other makes us think of laws and court rooms. Sure, folks may see superstitions as primitive (e.g., not eating a certain kind of meat on a particular day), but justice can be viewed as random too (e.g., why can we take fruit from a tree near us but one only a short distance away is forbidden?). We're used to rules of this sort, but, let's face it, there's nothing natural or inevitable about them.
Quote #6
But there is this material difference between superstition and justice, that the former is frivolous, useless, and burdensome; the latter is absolutely requisite to the well-being of mankind and existence of society. When we abstract from this circumstance [...] it must be confessed, that all regards to right and property, seem entirely without foundation, as much as the grossest and most vulgar superstition. (III.II.17)
Though superstition and justice appear to work in a similar way sometimes (and can seem equally random), Hume argues that there is a big difference: superstition is silly and useless while justice is a vital social structure. If we overlook this then, yeah, justice seems like another kind superstition.