Charles Ellicott Commentary 2 Samuel 15:34

"but if thou return to the city, and say unto Absalom, I will be thy servant, O king; as I have been thy father`s servant in time past, so will I now be thy servant; then wilt thou defeat for me the counsel of Ahithophel." — 2 Samuel 15:34 (ASV)

Say unto Absalom. — David here counsels fraud and treachery, and Hushai willingly accepts the part assigned to him, in order to thwart Ahithophel’s counsel and weaken Absalom’s rebellion. The narrative simply states the facts without justifying them. But while we cannot too strongly condemn such a stratagem, two things are to be remembered:

1. That like frauds in time of war and rebellion have been practised in all ages, and still continue.
2. That David and Hushai had but slender knowledge of the Divine revelation of truth and righteousness which enables us to condemn them, and, therefore, did with a clear conscience many things which we see to be wrong.