
Contrary to Christian apologists' assertions, humans do not get 'objective' morals from a god whose capricious whims determine right and wrong.
No matter how much C.S.Lewis tied himself into knots with his intellectual contortions, trying to prove that because he couldn't tell right from wrong, the god his mummy and daddy believed in must be real, the evidence of other cultures with other gods, and with none, shows that moral codes have broad principles common to all human cultures.
The rule probably most basic to all human cultures is the 'golden rule' - do as you would be done by or, as Christians would say, do unto others as you would have them do unto you. However, why people generally stick to this principle has been the subject of debate. Do they do it because of guilt, because we would feel bad about letting the other person down, or because of an innate sense of fairness where we want the fairest outcome.