So Lucy, 'splain something to me: how could a just God kill David's baby for his father's crimes?

Where do you get that God was disappointed? God was happy that Abraham was willing to do it, and changed the rules at the last minute when Abraham passed the test. It’s not that human sacrifice was wrong, it is just that God no longer commands it.

When did God give Abraham the “don’t kill people” command?

Never. Yahweh never outlaws murder until the giving Moses the Decalogue.

From this:

[QUOTE=Little Nemo]
God sighed in disappointment that Abraham didn’t get it and called off the actual murder.
[/QUOTE]

As for this,

[QUOTE=Little Nemo]
There’s a difference between a law and an order. You can be given an unlawful order even by somebody who enacted the law.
[/QUOTE]

That seems a very human, earthly way of looking at it. Yes, a military officer can give you an unlawful order that you should refuse, but he’s not the almighty ruler of the universe who made the rules and presumably is free to change his mind if he damn well feels like it.
It’s interesting to think that if God appeared on earth to you and told you something that you (the fallible, non-omniscient human) interpreted as contrary to the teachings of the Bible, you’d look God in the eye and tell him to screw off. Would you, really? You’d tell God he’s got it all wrong and you’re right?

Okay, no Bible scholar here. I was going on Little Nemo’s explanation of how God was just testing Abraham to see if he would kill the boy even though it was against the rules:

[QUOTE=Little Nemo]
The point of the story was that Abraham was supposed to defy God. He was supposed to tell God that murder was wrong even if an superior authority like God told you to do it. The lesson was supposed to be always follow God’s laws even if somebody else - even God himself - tells it’s okay to break them.
[/QUOTE]

We need a Rabbi.

I didn’t realize the the postings of Little Nemo had become holy writ about this story. I use the Dylan Highway 61 Revisited scriptures myself.
The question is whether God was disappointed that Abraham had listened to him, and nothing I see in the Bible, and nothing I learned in Hebrew School makes me think so. The moral of the story is that you should obey even the most heinous of commands and all will come out right.
I’m not sure what I would do talking to God but Abraham had a special relationship. Remember how he negotiated about the fate of Sodom? And Sarah laughed at the angel telling her that she was going to bear Isaac. So Abe saying “hey man, you must be putting me on” sounds perfectly feasible.