Albert Barnes Commentary 2 Samuel 18:13

"Otherwise if I had dealt falsely against his life (and there is no matter hid from the king), then thou thyself wouldest have set thyself against [me]." — 2 Samuel 18:13 (ASV)

The man gives a remarkable incidental testimony to David’s sagacity and insight (Compare to 2 Samuel 14:19), and to Joab’s known unscrupulousness.