And Absalom, and all the people the men of Israel, came to Jerusalem, and Ahithophel with him.

Jamieson-Fausset-Brown Bible Commentary

15-19. Hushai said unto Absalom, God save the king-Hushai's devotion to David was so well-known, that his presence in the camp of the conspirators excited great surprise. Professing, however, with great address, to consider it his duty to support the cause which the course of Providence and the national will had seemingly decreed should triumph, and urging his friendship for the father as a ground of confidence in his fidelity to the son, he persuaded Absalom of his sincerity, and was admitted among the councillors of the new king.

Matthew Henry's Concise Commentary

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!