Chuck's question is a good one. God is not of two minds. It's good for us to understand how his command regarding Isaac fits with his prohibition of murder. We don't want to simply dismiss such questions by suggesting God can make an executive decision that changes his ways whenever he wants. God doesn't do such things.
First, notice that God did not tell Abraham to murder Isaac or even to offer him as a child sacrifice. He told him to offer him as a burnt offering. This makes it (1) an act to bring propitiation for sin and (2) an act testing the entire consecration of the worshiper to the Lord. Not only does the text tell us this was such a test, Abraham also clearly understood it as such. He didn't believe he was taking Isaac's life for good, but rather that God intended to bring Isaac back to life (Hebrews 11:17-19) after testing Abraham's full devotion. The Bible never, anywhere, portrays this act as an attempted murder or child sacrifice; only as a great example of the full devotion to God represented by a burnt offering.
Second, the propitiatory nature of the burnt offering fits God's holiness. It shows how horribly serious sin is and how terrible the cost of paying for it is. The fact that all along God was not planning to go through with it, but rather to provide a weak substitute, only underscores the need for a sacrifice valuable enough to truly pay for sin. The whole incident points us to Christ, the Sacrifice of infinite value who finally did pay for the horrors of sin. So God's holiness, his perfect love, and his justice are all on display in this account. Far from undermining the moral character of God, this passage underscores its most central aspects.
Finally, we see here that the heart of the moral law is and always has been faith. Abraham's faith in God's promises (including his belief that his actions ultimately would not be murderous) is what makes his obedience righteous. God is not after a superficial, outward appearance of law-keeping, but rather a law-keeping that flows from a heart of faith.
The Isaac account is not about God's disregard for life, but rather about his loving determination to save us from sin and death, through faith in his Son. And the same could be said, obviously, about the death of Christ.