(I need a break from Russell, and I've meant to cover this topic for some time...)
Wikipedia describes this logical problem as "Is what is moral commanded by God because it is moral, or is it moral because it is commanded by God?"
This is partly misstated (logically self-contradicting) and partly a false dilemma (not either/or but both/and). At the same time, I believe I can avoid the tautology cited ("God is good, and good is God").
The first part is that "morality" is too vague a term. Modern man has divorced himself from morality, and thinks only in terms of legal and illegal. A more simple term is "good" (which I believe maintains the original argument).
So "Is what is good commanded by God because it is good, or is it good because it is commanded by God?"
The opposite of good is evil. But what is evil? Is killing evil? What about self-defense? Murder is killing, misused. Is sex evil? Rape is sex, misused. Is speaking evil? Lying is speech misused. Etc.
The notion of evil exists only as compared to what is good. That is, good exists. Evil cannot exist on its own. It exists only as a twisting or perversion of what is good. God is good, God exists. We exist, and demonstrate evil by disobeying God.
God's commands are good. Not just because God says so, or because they exist outside of God, or are the totality of God. The Law (the Ten Commandments) reveals God's nature. "Thou shalt not lie", because God is truth. "Thou shalt not murder", because God is life.
But God is more than the moral law. The law demands payment for infractions. God is merciful, in delaying punishment. God is gracious and loving in providing payment on our behalf.
In summary, "good" (or "moral") is what it is because it is a part of God (not all of God).
Further, without a notion of an absolute good (God), the notions of "good" and "evil" are meaningless.