The problem - sometimes referred to as the Euthyphro dilemma - was identified by Plato when he posed the question of "whether the gods love the pious because it is the pious, or whether the pious is pious only because it is loved by the gods". If god commands good things because they are intrinsically good then goodness exists independent of god and we can discover moral truth without him. If on the other hand things are good because god commands them then morality is not based on anything other than god's unpredictable whims.
I'm glad to see you've been reading Plato, Cofty. I've been banging on about his excellent philosophy for years on this forum. Euthyphro is one of his best dialogues about the ethical dilemma of a man taking his father to court for letting his slave die tied up in a ditch. There is so much discussion in that dialogue on what it means to be a good person. This from a man, Socrates, who is famously executed because he doesn't believe in the gods.
What we actually see is theists sanctifying ethical positions they arrived at by other means, claiming that their opinions reflect the goodness of god.
Yes exactly, five hundred years before Jesus the Greek philosophers were discussing what it means to be a moral person. Confucius and others introduced the Golden Rule (treat others as you would be treated) at around the same time. Theists have hijacked their ideas and ascribed them to a deity