21 Ahithophel told him, "Go and sleep with your father's concubines, for he has left them here to look after the palace. Then all Israel will know that you have insulted your father beyond hope of reconciliation, and they will throw their support to you."
Matthew Henry's Commentary on 2 Samuel 16:21
Commentary on 2 Samuel 16:15-23
(Read 2 Samuel 16:15-23)
The wisest counsellors of that age were Ahithophel and Hushai: Absalom thinks himself sure of success, when he has both; on them he relies, and consults not the ark, though he had that with him. But miserable counsellors were they both. Hushai would never counsel him to do wisely. Ahithophel counselled him to do wickedly; and so did as effectually betray him, as he did, who was designedly false to him: for they that advise men to sin, certainly advise them to their hurt. After all, honesty is the best policy, and will be found so in the long run. Ahithophel gave wicked counsel to Absalom; to render himself so hateful to his father, that he would never be reconciled to him; this cursed policy was of the devil. How desperately wicked is the human heart!