So if the civil laws show us the moral law, and the civil/judical laws are obligatory insofar as they embody the moral law, then the entire civil law is obligatory.
Not really. The moral law is also "a testimony of natural law and of that conscience which God has engraved upon the minds of men." (Calvin) For example, the penal sanctions are not obligatory. There's no mandate to execute Sabbath breakers or juvenile delinquents today. There is also no modern equivalent of the Canaanites and no Christian equivalent of jihad.
Bahnsen made that distinction on the Canaanites.
Also: We may build prisons and charge tariffs. We may license barbers, doctors and drivers. We may allow jury trial and a right to counsel. The police may arrest prostitutes and drug dealers. We can abolish slavery and polygamy. You get the idea.
Well, that's a different question altogether. The prison system is horribly unjust and makes the victim pay twice for the crime.