Ahithophel said to Absalom, “Go in to your father’s concubines that he has left to keep the house. Then all Israel will hear that you are abhorred by your father. Then the hands of all who are with you will be strong.” Bible

“go in to your father’s concubines.” Ahithophel advised Absalom to have sex with David’s concubines. Culturally, this would make an absolute break between Absalom and David, and show that Absalom was taking David’s place as king. However, Ahithophel’s advice may have had another motivation: Ahithophel was the grandfather of Bathsheba, whom David basically raped, got pregnant, arranged for her husband Uriah to be killed, and then married. Ahithophel may have thought of Absalom having sex with David’s wives as a kind of revenge. See commentary on 2 Samuel 15:12.

Commentary for: 2 Samuel 16:21