What the contextual nature of morality does and doesn't mean

We typically fine people occupying one of two extremes on the issue of moral relativism. Some people wish to impose rigid rules across all of time and space, regardless of circumstances: e.g., "The ancient Israelites were wicked because they practiced animal sacrifice." Others sense the (partially) historical character of right and wrong and leap from that genuine insight to the unwarranted conclusion that right and wrong are subjective, or whatever any particular society happens to deem them to be.

In Religion and Society, Collingwood explains why both extreme views are wrong:

"What is right for one society," we are told, "is wrong for another. It would be sadly narrow-minded to wish that every portion of the human race could live under the same kind of social organisation. On the contrary, to confer the blessings of civilisation upon the savage often means nothing but to force him into a mould for which he is quite unfitted and in which he can never be either happy or prosperous. His institutions are the best for him, and ours are the best for us ; and when we ask what is the right manner of life, the question always is, for whom? Nothing is right in itself, in isolation from the circumstances which make it right."

Much of this is perfectly true. Not only is one people's life not good for another people, but even one man's meat is another man's poison. Every race, every person, every situation is unique, presents unique problems and demands unique treatment. And if the argument means no more than that we must not impose the treatment proper to one case on another (as we frequently do), it is legitimate. But those who use it seem often to imply that, since every evil is relative to some situation, a perfectly free man who had no particular prejudices and no merely parochial interests would be superior to the distinction between good and bad. This of course is absurd ; for every man must be an individual and stand in some definite relation to other individuals ; and these relations will determine what is — and really is — right and wrong for him.

 And the Bible offers a perfect illustration of this point: Mosaic Law, which it was right for the Jews to obey, is no longer binding on Christians.

Right and wrong are dependent on historical circumstances. But what is right in a particular situation really is right, and what is wrong in that situation really is wrong.