If a man lies with his uncle’s wife, he has uncovered the nakedness of his uncle. They will bear their sin; they shall die childless.
Sins against the seventh commandment are here ordered to be severely punished. These are sins which, of all others, fools are most apt to make a mock at; but God would teach those the heinousness of the guilt by the extremity of the punishment that would not otherwise be taught it. I. Lying with another man's wife was made a capital crime.
Commenting on Leviticus 20:10-21
And if a man shall lie with his uncle's wife,.... His uncle being dead, and he marry her, which is forbidden, Lev 18:14, he hath uncovered his uncle's nakedness: his wife's, which was his, and therefore the kindred too near for a man to marry in, and such a copulation must be incestuous: they shall bear their sin; "both" of them, as the Vulgate Latin...
they shall die childless--Either by the judgment of God they shall have no children, or their spurious offspring shall be denied by human authority the ordinary privileges of children in Israel.