Charles Ellicott 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)

Against my own life. —The English, like the Vulgate, here follows the margin of the Hebrew; the Septuagint, in most manuscripts, following the text, has against his life. Either makes good sense, but the English is preferable. In this exchange, Joab thoroughly exposes his unscrupulous and self-willed character, and the man shows that he understood it.