Skeptics of Christianity sometimes claim that either God is subject to an external standard of justice and morality, or else whatever God arbitrarily says or does is the standard of justice and morality. Both of these choices are a problem, however, for the Christian.
If there is an external standard of justice, then God is not the ultimate being. There is a moral law that is greater than him. The Bible, however, rules that out.
If God can arbitrarily decide what is right and what is wrong, then justice and morality become meaningless because even though it is wrong to kill an innocent person today, tomorrow it could become OK, if God willed it to be. This idea, however, seems ludicrous as well.
The Christian answer to this dilemma is that God’s very nature is the Good and the Just. In other words, the moral law is built into God, and because God will always act according to his nature, the moral law will never change, and is thus not arbitrary. God is not subject to an external standard, because the standard is God himself.