On the other hand, if I had dealt treacherously against his life (and there is nothing hidden from the king), then you yourself would have stood aloof.”
Here is Absalom quite at a loss, at his wit's end first, and then at his life's end. He that began the fight, big with the expectation of triumphing over David himself, with whom, if he had had him in his power, he would not have dealt gently, is now in the greatest consternation, when he meets the servants of David, Sa2 18:9.
Commenting on 2 Samuel 18:9-18
Otherwise I should have wrought falsehood against mine own life,.... Or "soul"; he should not only have exposed his life to danger, but acted falsely to the king, by going contrary to his orders; yea, would have done that which was contrary to his own conscience; and if he had buoyed himself up with the hope of impunity, or of a reward, he should have...
Thou thyself wouldest have set thyself against me - This is a strong appeal to Joab's loyalty, and respect for the orders of David; but he was proof against every fine feeling, and against every generous sentiment.