There were a number of important aspects to the idea of sacred white womanhood in the South. Let us look at two of the most important of these.
First, there was the gender relations aspect of the idea. This held that women were to be put upon a pedestal by men. They were to be treated as fundamentally different from (and really morally better than) men. There was, for example, the idea that women were not interested in sex and that sex was a relatively dirty thing that only men were interested in. This put women above men.
Second, there was a racial aspect to this idea as well. There was a strong feeling that sacred white women needed to be protected from black men. This can be seen in films like Birth of a Nation and in books like To Kill a Mockingbird. It can also be seen in such real life horrors as the Emmett Till case. The idea that white women were sacred was seen by white men as another reason to keep blacks strongly subjugated.