Leviticus 18:9 - Exposition

In the third place, incest with a sister is forbidden, and it is specifically stated that under the term "sister" is meant the half-sister, the daughter of thy father, or … thy mother,… born at home , as would naturally be the case if she were the father's daughter, or born abroad , that is, the daughter of the mother by a previous marriage, when she belonged to a different household. Tamar's appeal to Amnon, "I pray thee speak unto the king; for he will not withhold me from thee," exhibits to us the poor woman grasping at any argument which might save her from her half-brother's brutality, and does not indicate that such marriages were, in the time of David, permissible ( 2 Samuel 13:29 ). The exact degree of relationship which existed between Abraham and Sarah is not altogether certain (cf. Genesis 20:12 with Genesis 11:29 ). Ezekiel reckons this sin in the catalogue of the iniquities of Jerusalem ( Ezekiel 22:11 ).