Where does morality come from?

Check out this article for a good introduction.

In a godless universe... Why is not helping the poor wrong? Why is not working and lying all day on the couch wrong? Why is murder wrong?

In a Christian universe, why is slavery wrong? Why is rape wrong? Why is genocide wrong? Why is cannibalism wrong? The Bible condones or enthusiastically endorses all of these crimes and many, many more. We could also ask the related question of why a man dating another man or a person wearing two kinds of fabric (among myriad other harmless things) are the moral failings the Bible claims they are.

You don't get your morality from your religion--you ascribe your morality to your religion. And without justification, since I'm sure your religion contradicts your morality in many ways. And that's true for essentially all Christians. In fact, few people even agree what constitutes Biblical morality, so it's inherently subjective.

It's just a matter of consensus.

Exactly. That's how human morality works. To say simply that something is "wrong" is actually saying that it's absolutely wrong, and since there is no absolute morality that's an inherent fallacy. You can only say it's wrong to you.

That's the very nature of subjective morality: you can judge anything and everything, whether now or in the past, according to the particular moral standards that make sense to you. You can also try to persuade others that your judgments are correct, as can anyone else. If enough people share the same judgments, they'll effectively become the moral standards of the culture. Until they change again. And at no point do they become objective moral standards, nor will they ever deserve to be shielded from questioning by you or anyone else.

That's the moral universe humans live in and have always lived in.