Albert Barnes Commentary Leviticus 20:17

"And if a man shall take his sister, his father`s daughter, or his mother`s daughter, and see her nakedness, and she see his nakedness; it is a shameful thing; and they shall be cut off in the sight of the children of their people: he hath uncovered his sister`s nakedness; he shall bear his iniquity." — Leviticus 20:17 (ASV)

Cut off ... - See Exodus 31:14 note. The more full expression here used probably refers to some special form of public excommunication, accompanied, it may be, by expulsion from the camp.