Now I think I understand.

I'll assume that God does whatever he wants, but he only wants to do things that are right and just.

The assumption behind the Commandment seems to be that earthly laws made by God's people will be just, because God inspires his people to do justice.

Thus, any legal distinction between murder and manslaughter (or no crime at all) ultimately derives from God and is presumed just.

In that case, God is not "bound" by man's laws. His will and those laws simply run parallel. The laws reflect his will. God's idea of "murder" should thus be the same as the state's - and vice versa.

> if God is not bound to agree with the state then it cannot be the state that determines whether a killing is murder or not.

The word "determine" is confusing. The state "determines" who does and does not deserve earthly punishment. God is the supreme judge who may agree or disagree with the state's verdict on an individual and "determine" his fate in that case.

So I don't understand how either the Commandment or the state's application of it takes away God's ability either to punish or to show mercy in specific cases.

God, not the state, is thus the absolute cosmic arbiter of an individual's guilt or innocence.

While the Commandments demand behavior that is pleasing to God and fundamental to society, no specific punishment is mentioned for violating them - except the inescapable and ultimate one of incurring God's wrath, and that could be experienced in any number of ways. Specific legal punishments are left to the king and the state. Evidently not all violations were traditionally punished by death.

God's Commandment forbids murder absolutely as an offense against God - but not battlefield killing or the death penalty. That's not to say that abolition of the death penalty, or the use of bean bags in war, would displease God, merely that the Commandment leaves those decisions to the state. Murder is an affront to God, but the death penalty isn't.   

That strikes many people as odd.

Note too that there are no Commandments against either slavery or torture. While that's not the same as recommending them, it seems to be a striking oversight, except that God doesn't make oversights. I'll let others others thrash out these problems.

P.S.: We're using logic to answer these questions. That's what Darwin used, and look where it got him. Does God not want us to use logic? Or just not to use it in matters of faith? But why should logic and faith, both instilled in us by God, ever contradict one another? (Whoa! There I go using logic again!)