From Leviticus 20:17 onwards, the way in which the laws are enforced is different. This may suggest a different level of seriousness towards the particular sin. Up to this point, for each infraction the guilty were put to death by the community after a proper inquiry was held. By way of contrast, the punishment for the next few violations is that the guilty is to be cut off.
17 “If a man takes his sister, a daughter of his father or a daughter of his mother, and sees her nakedness, and she sees his nakedness, it is a disgrace, and they shall be cut off in the sight of the children of their people. He has uncovered his sister’s nakedness, and he shall bear his iniquity.