Amasa went before them - Rather, “advanced to meet them.” Amasa was no doubt returning to Jerusalem, according to his orders 2 Samuel 20:4, and was probably much surprised to meet the army in march. Joab’s resolution was quickly taken.
And Joab’s garment ... - Render, “And Joab was girded with his military garment, as his clothing, and upon it” - i. e., the military garment - (or “him”), “the girdle of a sword fastened on his loins in its sheath, and as he went forth” (to meet Amasa) “it fell” out of the sheath. What appears to have happened is that, by accident or design, Joab’s sword fell out of the scabbard on the ground as he was going to meet Amasa, and that he picked it up with his left hand so as to have his right hand free for the customary salutation 2 Samuel 20:9. This awakened no suspicion in Amasa’s mind. Compare the case of Ehud, Judges 3:21.