Answer
Normally, we define murder as a subset of killing. Typically, when we speak of murder, we are speaking of the unlawful taking of a human life. We normally exclude from the definition of "murder" such things as the killing of animals, the lawful killing of human beings, and wartime deaths.
It is also important to note that the Bible defines good and evil, sin and righteousness, in terms of what God blesses and curses. That is, the only standard the Bible recognizes is God's own character. And God's blessing is clearest indication of what accords with God's character that the Bible gives us. Similarly, the clearest indication it provides of what is out of accord with God's character is God's curse. What God blesses is good; what he curses is evil. As a general rule, God curses what he prohibits and he blesses what he commands.
In the Bible, many types of killing are prohibited and cursed by God, while other types of killing are commanded and blessed by God. For instance, for many crimes the Bible advocates the death penalty as a righteous and sinless form of justice. Similarly, in holy war the slaying of soldiers and civilians alike was commanded by God. God generally cursed, however, the taking of a human life in anger or with malice aforethought.
In the particular case of Genesis 22, God instructed Abraham to kill Isaac. Because God commanded it, it was not sinful for Abraham to attempt to sacrifice Isaac. In fact, once Abraham proved his intention to sacrifice Isaac, God blessed him, demonstrating that Abraham had done the right thing.
I suppose one might object that it was wrong regardless of whether or not God commanded it, but that would miss the point of what I have just argued. Christian ethics recognize no standard for right and wrong higher than God himself. In the Christian system, to say that God is wrong or evil or sinful is false by definition. Whatever God is or does or says is good and just. If we disagree with his actions, it is we who are wrong, and our response should be to reevaluate our ethics and bring them in line with God's.
Then, too, there are ways we can harmonize the command to kill Isaac with what we know about God's character. Abraham did this, believing that Isaac would not remain dead (Gen. 22:5; Heb. 11:19). More importantly, Moses explicitly tells his readers that God commanded Abraham to kill Isaac as a test (Gen. 22:1), implying that God never really intended to let Isaac die. And of course, once Abraham passed the test, God stayed his hand and spared Isaac's life. In other words, the command to kill Isaac was not a revelation that God wanted Abraham to take Isaac's life, or that God demanded regular human sacrifice. It was merely a test of Abraham's faith and obedience. Such testing is completely compatible with the way God acts throughout the Bible.
Many examples of God doing questionable things can be found in Scripture. But, again, the biblical response is always that whatever God does sets the standard for right and wrong. If God does it and it looks sinful, then we need to alter our conception of sin.
Answer by Ra McLaughlin
Ra McLaughlin is Vice President of Finance and Administration at Third Millennium Ministries.