When people speak of morality, does it "always" stem from a divine being? That may be the prevailing sentiment in certain quarters, but there is a long and distinguished history of philosophers (many of them devout believers) who have argued that morality couldn't derive its authority from God.

Professor Gentzler has already directed you to Professor Brink's answer, but here is another way of looking at the problem. Consider the claim that killing is wrong because God forbids it in the Sixth Commandment. In order for God's command to create a genuine moral obligation (in this case, the obligation not to kill), God must possess a certain authority. (Otherwise anyone could issue commands and thereby create moral obligations!) But now the question immediately arises: whence comes this authority? God cannot establish his authority through another command, since he must already have authority in order for his commands to establish anything. Thus it seems that God's authority must come from somewhere else. There must, in other words, be a standard of moral authority that is independent of God's will.

I've often wondered whether anyone actually thinks that God's authority establishes moral principles. Of course, people say so. But when one asks such people why we ought to conform our behavior with the Divine Pronouncements, the answer, if it isn't to concede a moral standard independent of God's will, is usually that, otherwise, one will be cast into darkness with wailing and gnashing of teeth. But if so, then these aren't moral principles at all. They are arbitrary rules enforced through violence and fear.

To say so isn't to say that, for a believer, God need have nothing to do with morality. That God isn't the source of moral principles doesn't imply that God isn't an authority on moral truth in the sense that someone can be an authority on, say, mathematics. (Interesting ambiguity there.) It does imply, however, that if it is wrong to covet one's neighbor's ass, then there has to be a reason other than God's saying so that it's wrong to covet one's neighbor's ass.