Well, it was a test.
"How far will Abraham go? How deep is his commitment? I've got to find out. Hmmm... a test... a test... rock ridge... rock ridge..."
"I've got it!! I'll tell him to make his precious Isaac a burnt offering to me. We don't want him to actually go through with it and slaughter the lad, we just need to see if he would. It's a test, remember? Tell you what, if it looks like he's going all the way, pop up at the last minute and stop him. I'll make sure an animal appears nearby, a goat or sheep or something. Keep your eyes peeled for movement in the thicket. Now, let's get to work..."