But some people do hold that even the most clearly egregious rape or murder is wrong just as a matter of social consensus. its not "intrinsically" wrong (whatever that really means). That judgement of "wrong" is not backstopped by anything we'd call "absolute".
To expand on that 'social consensus'...it goes back to an inbuilt ability to empathise and a rather obvious sense of self preservation. So I won't kill an innocent person with premeditation because I don't want someone to do the same to me. I won't sexually assault someone without consent because I don't want to be sexually assaulted.
Now I don't work all this out every time something happens and I try to consider how allowing it might endanger me at some point. It's a gut feeling. I sense that X is wrong because I'm the descendent of a whole line of people who thought it was wrong. And we've outlived almost all of the people who thought it was OK. It's the way I'm built. It's in my dna. I have no more choice in the matter than I do as to whether I love my wife and my kids or not.
Allow me a quick diversion. It's almost universally accepted that incest is wrong. And by the luck of the evolutionary dice throw, some people thought it was OK and some people didn't. The latter have outlived the former. Their descendants are the ones that are here right now. And you don't have to know that incest causes genetic disorders to think that hey, there's something wrong with it.
But, that's the way biology works. Have sex with a close relative and you lineage is in danger. However, if biology worked differently and having sex with someone not related to you was a danger then incest would appear to be quite normal. Having sex outside the family would seem to be somewhat...icky.
Change the circumstances, change the context and you have to reconsider the act.
Other people think moral rules are established by a perfect lawgiver, so they call morality fundamentally "absolute" in principle, even if various complexities make judgement difficult sometimes.
And I think that as you said upstream, if it's a divine command then there has to be a reason for it being so. And if there's a good reason, then 'it is written' is as meaningless as saying you shouldn't murder someone because 'it is written'.
If someone tells me 'God says X is wrong' then I'll ask why He says that. If it's a good reason then I'll agree. If it isn't then I won't.