17 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. 18 If a man lies with a woman during her sickness and uncovers her nakedness, he has exposed her flow, and she has uncovered the flow of her blood. Both of them shall be cut off from their people. 19 You shall not uncover the nakedness of your mother's sister nor of your father's sister, for that would uncover his near of kin. They shall bear their guilt. 20 If a man lies with his uncle's wife, he has uncovered his uncle's nakedness. They shall bear their sin; they shall die childless. 21 If a man takes his brother's wife, it is an unclean thing. He has uncovered his brother's nakedness. They shall be childless.
Matthew Henry's Commentary on Leviticus 20:17-21
Commentary on Leviticus 20:10-27
(Read Leviticus 20:10-27)
These verses repeat what had been said before, but it was needful there should be line upon line. What praises we owe to God that he has taught the evil of sin, and the sure way of deliverance from it! May we have grace to adorn the doctrine of God our Saviour in all things; may we have no fellowship with unfruitful works of darkness, but reprove them.