Menstrual Impurity
Where this fits in the story: Leviticus 12 explicitly compares postpartum status with menstrual impurity, making Chapter 15 the fuller legal frame.
Where Scripture takes it next: No NT writer directly calls normal menstruation sinful or morally defiling.
Evidence boundary: Menstruation ≠ sin/shame; a morality claim would contradict the passage's category structure.