In the Law of Moses, the Lord spoke against the uncovering of a relative’s nakedness,
“If a man takes his sister, his father’s daughter or his mother’s daughter, and sees her nakedness and she sees his nakedness, it is a wicked thing. And they shall be cut off in the sight of their people. He has uncovered his sister’s nakedness. He shall bear his guilt. If a man lies with a woman during her sickness…You shall not uncover the nakedness of your mother’s sister nor of your father’s sister…If a man lies with his uncle’s wife…If a man takes his brother’s wife…” (Lev 20:17–21).
Those were all things that the Lord said were unclean, and any unclean Israelite could not approach the Lord, and in some cases, they had to give up their lives.
Christians must not defile themselves inwardly either, lest we not be able to approach our God.