Albert Barnes Commentary Leviticus 18:6

"None of you shall approach to any that are near of kin to him, to uncover [their] nakedness: I am Jehovah." — Leviticus 18:6 (ASV)

Near of kin — The term was evidently used to denote only those who came within certain limits of consanguinity, together with those who by affinity were regarded in the same relationship.

To uncover their nakedness — that is, to have sexual intercourse. The immediate object of this law was to forbid incest.