There is a brilliant post over on Reddit on how you don’t need a god to define morality and how taking the position that you do need said god actually weakens the definition of morality.
I think Christians are stuck on the horns of dilemma: is God good only because he defines what good is, or is he good because the things he does–the things he encourages and supports–are good in themselves? In other words, does God define “good” arbitrarily, or does he have a reason for saying that certain things are good?
Do you remember that episode of Friends where Joey needed money, and Chandler wanted to give it to him, but Joey refused to take charity? Chandler invented a card game called “Cups” that had arbitrary rules he thought up on the spot so he would “lose” money to Joey. You weren’t surprised when Chandler managed to “lose” exactly the amount of money he intended to give to Joey: Chandler made the rules, so of course he did what he set out to accomplish when he invented the game.
The choice of analogy for his explanation is spot on, and I highly recommend you check out the entire post here.