20 Then Absalom said to Ahithophel, "Give your counsel. What shall we do?" 21 Ahithophel said to Absalom, "Go in to your father's concubines, whom he has left to keep the house, and all Israel will hear that you have made yourself a stench to your father, and the hands of all who are with you will be strengthened." 22 So they pitched a tent for Absalom on the roof. And Absalom went in to his father's concubines in the sight of all Israel. 23 Now in those days the counsel that Ahithophel gave was as if one consulted the word of God; so was all the counsel of Ahithophel esteemed, both by David and by Absalom.
Matthew Henry's Commentary on 2 Samuel 16:20-37
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!