The funny thing about morality and the Abrahamic religions is that it seems as though it was intended for humans not to have a moral compass. (Read Genesis)
We were supposed to blindly follow orders given, hence why I think Eve listened to the Serpent when he told her she would know what good and evil were.
To answer the question; morals are subjective and more of a social construct. This is not to say that they're meaningless, but that we make them and that we ultimately decide ourselves what's 'right' and 'wrong'. As broad a spectrum it can be seen as, most modern and civil societies agree on the most part on a basic 'do's and don'ts'. I'd say it's because we as animals along with any other living species have a duty to pass our genes on as much as possible.