I feel like there are more interesting parallels to look at in the idea of self-contained systems.
Both our legal and religious structures are essentially societal codes, right? They're a collection of ideas that we've codified into a structure that gives them the authority to carry out their mandates.
We accept forms of collective governance that make sense to us. We might quibble about the details of implementation, but most rational people will agree we need some kind of public cooperation, be it roads, telecommunication networks, political structures, etc.
Atheists would disagree, but most believers in a religion would take the position that the moral good from their religiousness outweighs the drawbacks (i.e. some of us are a bit too enthusiastic).
kda @22 pointed out that bookkeeping, religion and government all started to get organised around about the time they could write things down. There are some good thoughts to be had over how much our tendencies to organise, group, and heuristic our way through life influenced those early-civilisation developments.
If 'all governments are theocracies' is true, then 'all theocracies are governments' also holds true. The application of theocracy looks a lot like the application of government.
TL,DR: government and justice are both organised ideas.
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