Then it becomes completely meaningless - It's the equivalent to saying to someone - "Be good" without defining anything about what good-ness involves.
Once you start defining specifically what you mean by good, if your initial premise falls apart and there's no practical way to be good, then what's the point of saying be good?
Once you start defining specifically what you mean by good, if your initial premise falls apart and there's no practical way to be good, then what's the point of saying be good?