In short, the answer to the above question is this: as humans, we generally don't dig it if someone murders us, rapes us, steals from us or burns our house to the ground. So as a society we have, over time, agreed to not do this to one another (because if I do it to you, you then can do it to me), and have decided to punish those who transgress anyway. We don't need God in order to understand this. We're not born understanding right and wrong--it comes as a result of being able to think and reason and understand that if I do this to that person, than he can turn around and do it to me, and I don't want that done to me, so I'd better not do that to him. This is the simplified idea of a society with law and order. Even animals do this.
But if you still believe that morality comes from God, then you must ask yourselves the next questions. Which God from which religion, and from which flavor of a particular religion? Is it Zeus you follow? Mithra? Jesus? Allah? Yahweh? If Christianity is your religion of choice, who is your leader?--Joseph Smith, Martin Luther, Benedict XVI? And if you've chosen Christianity, you need to justify why you've chosen one church over the other. If you've chosen Catholicism over Anglicanism, or Southern Baptist over Mormonism, it must be because you believe that your particular choice has it more right than any other. But why? Didn't you exercise your own intellect and come to that observation yourself? Either way, you still make some choices on morality based on your own reasoning.
Christopher Hitchens makes a rather simple and eloquent statement about the origin of morality, and I'm going to share it now.
"Answer me this if you think morality comes from the supernatural and we require celestial dictatorship permission for it. Name me a moral action committed by a believer, or a moral statement or an ethical statement uttered by one, that could not be made or uttered by a non-believer....If I was to ask anyone in this room, however, could they name a wicked action performed or a vile statement made by someone attributable only to their religious faith, there isn't a single person here who'd have to hesitate for a second in discovering what that was and saying it."
In addition to this idea, there could be volumes of books written on the many reasons why "God" is actually quite immoral, but that's a whole other post entirely (or several). What Hitchens successfully says is that if murder/theft/rape/etc is inherently wrong as prohibited by God, why can both a believer and non-believer agree on this? Why can obscure aboriginal tribes come to this conclusion without so much as hearing of Jesus or Allah or Yahweh? Because basic, fundamental morality is universal and a common desire to all human beings.