Leviticus 18:7
The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she is thy mother; thou shalt not uncover her nakedness. The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she is thy mother; thou shalt not uncover her nakedness.
Sexual familiarity and the uncovering of nakedness between men and women are forbidden, with the extended list in Leviticus 18:6-19 defining the prohibited relations. The prohibition forms a boundary set to preserve the clean and pure virtues of God's people. To engage in such conduct is both a crime and a sin that breaks through and violates those boundaries.